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Linux kernel mirror (for testing) git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
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SPDX-License-Identifier: GPL-2.0-or-later/* * fs/eventpoll.c (Efficient event retrieval implementation) * Copyright (C) 2001,...,2009 Davide Libenzi * * Davide Libenzi <davidel@xmailserver.org> */
#include <linux/init.h>#include <linux/kernel.h>#include <linux/sched/signal.h>#include <linux/fs.h>#include <linux/file.h>#include <linux/signal.h>#include <linux/errno.h>#include <linux/mm.h>#include <linux/slab.h>#include <linux/poll.h>#include <linux/string.h>#include <linux/list.h>#include <linux/hash.h>#include <linux/spinlock.h>#include <linux/syscalls.h>#include <linux/rbtree.h>#include <linux/wait.h>#include <linux/eventpoll.h>#include <linux/mount.h>#include <linux/bitops.h>#include <linux/mutex.h>#include <linux/anon_inodes.h>#include <linux/device.h>#include <linux/uaccess.h>#include <asm/io.h>#include <asm/mman.h>#include <linux/atomic.h>#include <linux/proc_fs.h>#include <linux/seq_file.h>#include <linux/compat.h>#include <linux/rculist.h>#include <linux/capability.h>#include <linux/seqlock.h>#include <net/busy_poll.h>
/* * fs/eventpoll.c - Efficient event polling ("epoll") kernel implementation. * * * Overview * -------- * * Each epoll_create(2) returns an anonymous [eventpoll] file whose * ->private_data is a struct eventpoll. Each EPOLL_CTL_ADD installs * a struct epitem linking one (watched file, fd) pair back to that * eventpoll via the watched file's f_op->poll() wait queue(s). When * the watched file signals readiness, ep_poll_callback() fires and * marks the epitem ready. epoll_wait(2) drains the ready list under * ep->mtx, re-queueing items in level-triggered mode. * * epoll instances can watch other epoll instances up to EP_MAX_NESTS * deep; cycles are forbidden and detected at EPOLL_CTL_ADD time. * * * Locking * ------- * * Three levels, acquired from outer to inner: * * epnested_mutex (global; rare; taken only for EPOLL_CTL_ADD * loop / path checks) * > ep->mtx (per-eventpoll; sleepable; serializes most ops) * > ep->lock (per-eventpoll; IRQ-safe spinlock) * * file->f_lock (per-file; NOT IRQ-safe; guards f_ep hlist ops; * nested inside ep->mtx, outside ep->lock) * * Rationale: * - ep->lock is a spinlock because ep_poll_callback() is called from * wake_up() which may run in hard-IRQ context. All ep->lock * critical sections use spin_lock_irqsave(). * - ep->mtx is a sleepable mutex because the event delivery loop * calls copy_to_user(), and ep_insert() may sleep in * kmem_cache_alloc() and f_op->poll(). * - epnested_mutex is global because cycle detection needs a global * view of the epoll topology; a per-object scheme would let two * concurrent inserts (A into B, B into A) construct a cycle * without either observer seeing it. * - Per-ep ep->mtx is preferred for scalability elsewhere. Events * that require epnested_mutex are rare. * * When EPOLL_CTL_ADD nests one eventpoll inside another we acquire * ep->mtx on both: outer first, target second. Since cycles are * forbidden the set of live ep->mtx holds is always a strict chain, * communicated to lockdep via mutex_lock_nested() subclasses derived * from the current recursion depth. * * * Field protection * ---------------- * * struct eventpoll: * mtx - self * rbr - ep->mtx * ovflist, rdllist - ep->lock (IRQ-safe) * wq - ep->lock for queue mutation * poll_wait - internal waitqueue spinlock * refs - file->f_lock for adds; ep->mtx for removes; * RCU for readers (hlist_del_rcu + kfree_rcu(ep)) * ws - ep->mtx * gen, loop_check_depth - epnested_mutex * file, user - immutable after setup * refcount - atomic (refcount_t) * napi_* - READ_ONCE / WRITE_ONCE * * struct epitem: * rbn / rcu union - rbn: ep->mtx (while epi is linked in ep->rbr). * rcu: written only by kfree_rcu(epi) on the free * path; otherwise untouched by epoll code. * rdllink, next - ep->lock * ffd, ep - immutable after ep_insert() * pwqlist - ep->mtx for writes; POLLFREE clears pwq->whead * via smp_store_release(), see below * fllink - file->f_lock for mutation; hlist_del_rcu + * kfree_rcu(epi) for safe RCU readers * ws - RCU (rcu_assign_pointer / * rcu_dereference_check(mtx)) * event - ep->mtx for writes; lockless read in * ep_poll_callback pairs with smp_mb() in * ep_modify() * * * Ready-list state machine * ------------------------ * * Readiness is tracked in two lists under ep->lock: * * rdllist - doubly-linked FIFO; the "current" ready list. * ovflist - singly-linked LIFO; used during a scan to catch * events that arrive while rdllist is being iterated * without ep->lock. * * Encoded in ep->ovflist: * EP_UNACTIVE_PTR - no scan active; callback appends to rdllist. * NULL - scan active, no spill yet. * pointer to epi - scan active with spilled items (LIFO). * * Encoded in epi->ovflist_next: * EP_UNACTIVE_PTR - epi is not on ovflist. * otherwise - next epi on ovflist (NULL at tail). * * ep_start_scan() flips "not scanning" to "scanning" and splices * rdllist into a caller-local scan_batch. ep_done_scan() drains ovflist * back to rdllist (list_add head-insert reverses LIFO to FIFO), * flips back to "not scanning", and re-splices any items the caller * left in scan_batch (e.g., level-triggered re-queues). * * * Removal paths * ------------- * * Three paths dispose of epitems and/or eventpolls: * * A. ep_remove() - EPOLL_CTL_DEL and ep_insert() * rollback. Caller holds ep->mtx. * B. ep_clear_and_put() - close of the epoll fd itself * (ep_eventpoll_release). * C. eventpoll_release_file() - close of a watched file, invoked * from __fput(). * * Coordination: * A and C exclude each other via the watched file's refcount. * A pins the file with epi_fget() before touching file->f_ep or * file->f_lock; if the pin fails, __fput() is in flight and C * will clean this epi up. See the epi_fget() block comment. * A and B both hold ep->mtx serially. B walks the rbtree with * rb_next() captured before ep_remove() erases the current node. * B and C both take ep->mtx; the loser sees fewer entries or an * empty file->f_ep. * * Within every path the internal order is strict: * ep_unregister_pollwait() - drain pwqlist; synchronizes with any * in-flight ep_poll_callback via the * watched wait-queue head's lock. * ep_remove_file() - hlist_del_rcu of epi->fllink and, * if last watcher, clear file->f_ep, * under file->f_lock. * ep_remove_epi() - rb_erase, rdllist unlink (ep->lock), * wakeup_source_unregister, * kfree_rcu(epi). * * kfree_rcu(epi) defers the free past RCU readers in * reverse_path_check_proc(); kfree_rcu(ep) defers past readers in * ep_get_upwards_depth_proc(). * * * POLLFREE handshake * ------------------ * * When a subsystem tears down a wait-queue head that an epitem is * registered on (binder, signalfd, ...), it wakes the callback with * POLLFREE and must RCU-defer the head's free. The store/load pair: * * ep_poll_callback() POLLFREE branch: * smp_store_release(&pwq->whead, NULL) * * ep_remove_wait_queue(): * smp_load_acquire(&pwq->whead) * * See those sites for the full argument. */
/* Epoll private bits inside the event mask */#define EP_PRIVATE_BITS (EPOLLWAKEUP | EPOLLONESHOT | EPOLLET | EPOLLEXCLUSIVE)
#define EPOLLINOUT_BITS (EPOLLIN | EPOLLOUT)
#define EPOLLEXCLUSIVE_OK_BITS (EPOLLINOUT_BITS | EPOLLERR | EPOLLHUP | \ EPOLLWAKEUP | EPOLLET | EPOLLEXCLUSIVE)
/* Maximum number of nesting allowed inside epoll sets */#define EP_MAX_NESTS 4
#define EP_MAX_EVENTS (INT_MAX / sizeof(struct epoll_event))
#define EP_UNACTIVE_PTR ((void *) -1L)
#define EP_ITEM_COST (sizeof(struct epitem) + sizeof(struct eppoll_entry))
/* Wait structure used by the poll hooks */struct eppoll_entry { /* List header used to link this structure to the "struct epitem" */ struct eppoll_entry *next;
/* The "base" pointer is set to the container "struct epitem" */ struct epitem *base;
/* * Wait queue item that will be linked to the target file wait * queue head. */ wait_queue_entry_t wait;
/* The wait queue head that linked the "wait" wait queue item */ wait_queue_head_t *whead;};
/* * Each file descriptor added to the eventpoll interface will * have an entry of this type linked to the "rbr" RB tree. * Avoid increasing the size of this struct, there can be many thousands * of these on a server and we do not want this to take another cache line. */struct epitem { union { /* RB tree node links this structure to the eventpoll RB tree */ struct rb_node rbn; /* Used to free the struct epitem */ struct rcu_head rcu; };
/* Link on the owning eventpoll's ready list (ep->rdllist). */ struct list_head rdllink;
/* * Link on the owning eventpoll's scan-overflow list (ep->ovflist), * EP_UNACTIVE_PTR when not linked. See epi_on_ovflist() / * epi_clear_ovflist() and the "Ready-list state machine" section * in the top-of-file banner. */ struct epitem *ovflist_next;
/* The file descriptor information this item refers to */ struct epoll_key ffd;
/* List containing poll wait queues */ struct eppoll_entry *pwqlist;
/* The "container" of this item */ struct eventpoll *ep;
/* List header used to link this item to the "struct file" items list */ struct hlist_node fllink;
/* wakeup_source used when EPOLLWAKEUP is set */ struct wakeup_source __rcu *ws;
/* The structure that describe the interested events and the source fd */ struct epoll_event event;};
/* * This structure is stored inside the "private_data" member of the file * structure and represents the main data structure for the eventpoll * interface. */struct eventpoll { /* * This mutex is used to ensure that files are not removed * while epoll is using them. This is held during the event * collection loop, the file cleanup path, the epoll file exit * code and the ctl operations. */ struct mutex mtx;
/* Wait queue used by sys_epoll_wait() */ wait_queue_head_t wq;
/* Wait queue used by file->poll() */ wait_queue_head_t poll_wait;
/* List of ready file descriptors */ struct list_head rdllist;
/* Lock which protects rdllist and ovflist */ spinlock_t lock;
/* Protect switching between rdllist and ovflist */ seqcount_spinlock_t seq;
/* RB tree root used to store monitored fd structs */ struct rb_root_cached rbr;
/* * This is a single linked list that chains all the "struct epitem" that * happened while transferring ready events to userspace w/out * holding ->lock. */ struct epitem *ovflist;
/* wakeup_source used when ep_send_events or __ep_eventpoll_poll is running */ struct wakeup_source *ws;
/* The user that created the eventpoll descriptor */ struct user_struct *user;
struct file *file;
/* used to optimize loop detection check */ u64 gen; struct hlist_head refs; u8 loop_check_depth;
/* usage count, orchestrates "struct eventpoll" disposal */ refcount_t refcount;
/* used to defer freeing past ep_get_upwards_depth_proc() RCU walk */ struct rcu_head rcu;
#ifdef CONFIG_NET_RX_BUSY_POLL /* used to track busy poll napi_id */ unsigned int napi_id; /* busy poll timeout */ u32 busy_poll_usecs; /* busy poll packet budget */ u16 busy_poll_budget; bool prefer_busy_poll;#endif
#ifdef CONFIG_DEBUG_LOCK_ALLOC /* tracks wakeup nests for lockdep validation */ u8 nests;#endif};
/* Wrapper struct used by poll queueing */struct ep_pqueue { poll_table pt; struct epitem *epi;};
/* * Configuration options available inside /proc/sys/fs/epoll/ *//* Maximum number of epoll watched descriptors, per user */static long max_user_watches __read_mostly;
/* * Cycle and path-length checks at EPOLL_CTL_ADD * --------------------------------------------- * * When EPOLL_CTL_ADD creates a link that either targets an eventpoll * file or extends an existing chain of eventpolls, two checks run: * * 1. no cycle is being formed -- ep_loop_check() walks downward * from the candidate target, and ep_get_upwards_depth_proc() * walks upward from the outer ep, both bounded by EP_MAX_NESTS. * 2. no file accumulates more than path_limits[depth] wakeup paths * of a given length -- reverse_path_check(). * * Both need a global view of the epoll topology and must be atomic * with the insertion, so the check is serialized by epnested_mutex * and carries its scratch state on a stack-allocated struct * ep_ctl_ctx scoped to one do_epoll_ctl() call. Non-nested inserts * skip this machinery entirely and take only ep->mtx. * * epnested_mutex Serializes the whole check. * loop_check_gen Global monotonic stamp, bumped at the start of * a check and again at the end. ep->gen caches * the value under which ep was last visited by * ep_loop_check_proc() or * ep_get_upwards_depth_proc(); the post-check * bump ensures those cached stamps can no longer * equal loop_check_gen, so the * "ep->gen == loop_check_gen" trigger in * ep_ctl_lock() only fires while another check * is in flight. * * struct ep_ctl_ctx carries the rest (inserting_into, tfile_check_list, * path_count[]) through the walk; see its declaration below. * * Commits fdcfce93073d ("eventpoll: Fix integer overflow in * ep_loop_check_proc()") and f2e467a48287 ("eventpoll: Fix * semi-unbounded recursion") hardened the walk; any refactor must * preserve both bail-outs. */static DEFINE_MUTEX(epnested_mutex);static u64 loop_check_gen = 0;
#define PATH_ARR_SIZE 5
/* * Per-do_epoll_ctl() scratch for the loop / path checks. Allocated on * the caller's stack; populated by ep_ctl_lock() and the downward * walk; consumed by reverse_path_check(); released by ep_ctl_unlock(). * Only valid while the caller holds epnested_mutex. */struct ep_ctl_ctx { /* * Outer eventpoll for one ep_loop_check(); if the downward walk * reaches it the insert would form a cycle. */ struct eventpoll *inserting_into;
/* * Singly-linked list of epitems_head objects collected during * ep_loop_check_proc(), then walked by reverse_path_check(). * Terminated by EP_UNACTIVE_PTR, not NULL: epitems_head->next * doubles as a membership flag (a NULL ->next means "not on this * list", see ep_remove_file()), so the list uses a non-NULL * sentinel to keep the tail head distinguishable from an unlisted * one. */ struct epitems_head *tfile_check_list;
/* * Per-depth wakeup-path tally used by reverse_path_check_proc(); * reinitialized to zero at the start of each reverse_path_check() * iteration. */ int path_count[PATH_ARR_SIZE];};
/* Slab cache used to allocate "struct epitem" */static struct kmem_cache *epi_cache __ro_after_init;
/* Slab cache used to allocate "struct eppoll_entry" */static struct kmem_cache *pwq_cache __ro_after_init;
/* * Wrapper anchor for file->f_ep when the watched file is not itself an * eventpoll; for the epoll-watches-epoll case, file->f_ep points at * &watched_ep->refs directly. The ->next field threads * ctx->tfile_check_list during one EPOLL_CTL_ADD path check. The ->file * field holds a reference to the associated file while the head is on * the list. */struct epitems_head { struct hlist_head epitems; struct epitems_head *next; struct file *file;};
static struct kmem_cache *ephead_cache __ro_after_init;
static inline void free_ephead(struct epitems_head *head){ if (head) kmem_cache_free(ephead_cache, head);}
static void list_file(struct file *file, struct ep_ctl_ctx *ctx){ struct epitems_head *head;
head = container_of(file->f_ep, struct epitems_head, epitems); if (!head->next) { /* * The caller owns a reference to @file or holds the ep->mtx for the * epitem that led here. The latter blocks eventpoll_release_file() * before the file allocation can be freed and reused. A dying leaf * can be skipped since removing links cannot increase the reverse * path count. */ if (!file_ref_get(&file->f_ref)) return; head->file = file; head->next = ctx->tfile_check_list; ctx->tfile_check_list = head; }}
static void unlist_file(struct epitems_head *head){ struct epitems_head *to_free = head; struct hlist_node *p = rcu_dereference(hlist_first_rcu(&head->epitems)); struct file *file = head->file; if (p) { struct epitem *epi= container_of(p, struct epitem, fllink); spin_lock(&epi->ffd.file->f_lock); if (!hlist_empty(&head->epitems)) to_free = NULL; head->next = NULL; head->file = NULL; spin_unlock(&epi->ffd.file->f_lock); } free_ephead(to_free); fput(file);}
#ifdef CONFIG_SYSCTL
#include <linux/sysctl.h>
static long long_zero;static long long_max = LONG_MAX;
static const struct ctl_table epoll_table[] = { { .procname = "max_user_watches", .data = &max_user_watches, .maxlen = sizeof(max_user_watches), .mode = 0644, .proc_handler = proc_doulongvec_minmax, .extra1 = &long_zero, .extra2 = &long_max, },};
static void __init epoll_sysctls_init(void){ register_sysctl("fs/epoll", epoll_table);}#else#define epoll_sysctls_init() do { } while (0)#endif /* CONFIG_SYSCTL */
static const struct file_operations eventpoll_fops;
bool is_file_epoll(struct file *f){ return f->f_op == &eventpoll_fops;}
/* Compare RB tree keys */static inline int ep_cmp_ffd(struct epoll_key *p1, struct epoll_key *p2){ return (p1->file > p2->file ? +1: (p1->file < p2->file ? -1 : p1->fd - p2->fd));}
/* True iff @epi is on its owning ep's ready list. */static inline bool ep_is_linked(struct epitem *epi){ return !list_empty(&epi->rdllink);}
static inline struct eppoll_entry *ep_pwq_from_wait(wait_queue_entry_t *p){ return container_of(p, struct eppoll_entry, wait);}
/* Get the "struct epitem" from a wait queue pointer */static inline struct epitem *ep_item_from_wait(wait_queue_entry_t *p){ return container_of(p, struct eppoll_entry, wait)->base;}
/* * Ready-list / ovflist state (see "Ready-list state machine" in the * top-of-file banner for the full state machine). EP_UNACTIVE_PTR is * the sentinel; these wrappers name each transition and each test so * call sites do not need to know the sentinel's value. */
/* True iff @ep is between ep_enter_scan() and ep_exit_scan(). */static inline bool ep_is_scanning(struct eventpoll *ep){ return READ_ONCE(ep->ovflist) != EP_UNACTIVE_PTR;}
/* Called by ep_start_scan(): divert ep_poll_callback() to ovflist. */static inline void ep_enter_scan(struct eventpoll *ep){ WRITE_ONCE(ep->ovflist, NULL);}
/* Called by ep_done_scan(): redirect ep_poll_callback() back to rdllist. */static inline void ep_exit_scan(struct eventpoll *ep){ WRITE_ONCE(ep->ovflist, EP_UNACTIVE_PTR);}
/* True iff @epi is currently linked on its ep's ovflist. */static inline bool epi_on_ovflist(const struct epitem *epi){ return epi->ovflist_next != EP_UNACTIVE_PTR;}
/* Mark @epi as not on any ovflist (init and post-drain). */static inline void epi_clear_ovflist(struct epitem *epi){ epi->ovflist_next = EP_UNACTIVE_PTR;}
/* True iff @ep has ready events that epoll_wait() might harvest. */static inline bool ep_events_available(struct eventpoll *ep){ unsigned int seq = read_seqcount_begin(&ep->seq);
return !list_empty_careful(&ep->rdllist) || ep_is_scanning(ep) || read_seqcount_retry(&ep->seq, seq);}
#ifdef CONFIG_NET_RX_BUSY_POLL/** * busy_loop_ep_timeout - check if busy poll has timed out. The timeout value * from the epoll instance ep is preferred, but if it is not set fallback to * the system-wide global via busy_loop_timeout. * * @start_time: The start time used to compute the remaining time until timeout. * @ep: Pointer to the eventpoll context. * * Return: true if the timeout has expired, false otherwise. */static bool busy_loop_ep_timeout(unsigned long start_time, struct eventpoll *ep){ unsigned long bp_usec = READ_ONCE(ep->busy_poll_usecs);
if (bp_usec) { unsigned long end_time = start_time + bp_usec; unsigned long now = busy_loop_current_time();
return time_after(now, end_time); } else { return busy_loop_timeout(start_time); }}
static bool ep_busy_loop_on(struct eventpoll *ep){ return !!READ_ONCE(ep->busy_poll_usecs) || READ_ONCE(ep->prefer_busy_poll) || net_busy_loop_on();}
static bool ep_busy_loop_end(void *p, unsigned long start_time){ struct eventpoll *ep = p;
return ep_events_available(ep) || busy_loop_ep_timeout(start_time, ep);}
/* * Busy poll if globally on and supporting sockets found && no events, * busy loop will return if need_resched or ep_events_available. * * we must do our busy polling with irqs enabled */static bool ep_busy_loop(struct eventpoll *ep){ unsigned int napi_id = READ_ONCE(ep->napi_id); u16 budget = READ_ONCE(ep->busy_poll_budget); bool prefer_busy_poll = READ_ONCE(ep->prefer_busy_poll);
if (!budget) budget = BUSY_POLL_BUDGET;
if (napi_id_valid(napi_id) && ep_busy_loop_on(ep)) { napi_busy_loop(napi_id, ep_busy_loop_end, ep, prefer_busy_poll, budget); if (ep_events_available(ep)) return true; /* * Busy poll timed out. Drop NAPI ID for now, we can add * it back in when we have moved a socket with a valid NAPI * ID onto the ready list. */ if (prefer_busy_poll) napi_resume_irqs(napi_id); ep->napi_id = 0; return false; } return false;}
/* * Set epoll busy poll NAPI ID from sk. */static inline void ep_set_busy_poll_napi_id(struct epitem *epi){ struct eventpoll *ep = epi->ep; unsigned int napi_id; struct socket *sock; struct sock *sk;
if (!ep_busy_loop_on(ep)) return;
sock = sock_from_file(epi->ffd.file); if (!sock) return;
sk = sock->sk; if (!sk) return;
napi_id = READ_ONCE(sk->sk_napi_id);
/* Non-NAPI IDs can be rejected * or * Nothing to do if we already have this ID */ if (!napi_id_valid(napi_id) || napi_id == ep->napi_id) return;
/* record NAPI ID for use in next busy poll */ ep->napi_id = napi_id;}
static long ep_eventpoll_bp_ioctl(struct file *file, unsigned int cmd, unsigned long arg){ struct eventpoll *ep = file->private_data; void __user *uarg = (void __user *)arg; struct epoll_params epoll_params;
switch (cmd) { case EPIOCSPARAMS: if (copy_from_user(&epoll_params, uarg, sizeof(epoll_params))) return -EFAULT;
/* pad byte must be zero */ if (epoll_params.__pad) return -EINVAL;
if (epoll_params.busy_poll_usecs > S32_MAX) return -EINVAL;
if (epoll_params.prefer_busy_poll > 1) return -EINVAL;
if (epoll_params.busy_poll_budget > NAPI_POLL_WEIGHT && !capable(CAP_NET_ADMIN)) return -EPERM;
WRITE_ONCE(ep->busy_poll_usecs, epoll_params.busy_poll_usecs); WRITE_ONCE(ep->busy_poll_budget, epoll_params.busy_poll_budget); WRITE_ONCE(ep->prefer_busy_poll, epoll_params.prefer_busy_poll); return 0; case EPIOCGPARAMS: memset(&epoll_params, 0, sizeof(epoll_params)); epoll_params.busy_poll_usecs = READ_ONCE(ep->busy_poll_usecs); epoll_params.busy_poll_budget = READ_ONCE(ep->busy_poll_budget); epoll_params.prefer_busy_poll = READ_ONCE(ep->prefer_busy_poll); if (copy_to_user(uarg, &epoll_params, sizeof(epoll_params))) return -EFAULT; return 0; default: return -ENOIOCTLCMD; }}
static void ep_suspend_napi_irqs(struct eventpoll *ep){ unsigned int napi_id = READ_ONCE(ep->napi_id);
if (napi_id_valid(napi_id) && READ_ONCE(ep->prefer_busy_poll)) napi_suspend_irqs(napi_id);}
static void ep_resume_napi_irqs(struct eventpoll *ep){ unsigned int napi_id = READ_ONCE(ep->napi_id);
if (napi_id_valid(napi_id) && READ_ONCE(ep->prefer_busy_poll)) napi_resume_irqs(napi_id);}
#else
static inline bool ep_busy_loop(struct eventpoll *ep){ return false;}
static inline void ep_set_busy_poll_napi_id(struct epitem *epi){}
static long ep_eventpoll_bp_ioctl(struct file *file, unsigned int cmd, unsigned long arg){ return -EOPNOTSUPP;}
static void ep_suspend_napi_irqs(struct eventpoll *ep){}
static void ep_resume_napi_irqs(struct eventpoll *ep){}
#endif /* CONFIG_NET_RX_BUSY_POLL */
/* * As described in commit 0ccf831cb lockdep: annotate epoll * the use of wait queues used by epoll is done in a very controlled * manner. Wake ups can nest inside each other, but are never done * with the same locking. For example: * * dfd = socket(...); * efd1 = epoll_create(); * efd2 = epoll_create(); * epoll_ctl(efd1, EPOLL_CTL_ADD, dfd, ...); * epoll_ctl(efd2, EPOLL_CTL_ADD, efd1, ...); * * When a packet arrives to the device underneath "dfd", the net code will * issue a wake_up() on its poll wake list. Epoll (efd1) has installed a * callback wakeup entry on that queue, and the wake_up() performed by the * "dfd" net code will end up in ep_poll_callback(). At this point epoll * (efd1) notices that it may have some event ready, so it needs to wake up * the waiters on its poll wait list (efd2). So it calls ep_poll_safewake() * that ends up in another wake_up(), after having checked about the * recursion constraints. That are, no more than EP_MAX_NESTS, to avoid * stack blasting. * * When CONFIG_DEBUG_LOCK_ALLOC is enabled, make sure lockdep can handle * this special case of epoll. */#ifdef CONFIG_DEBUG_LOCK_ALLOC
static void ep_poll_safewake(struct eventpoll *ep, struct epitem *epi, unsigned pollflags){ struct eventpoll *ep_src; unsigned long flags; u8 nests = 0;
/* * To set the subclass or nesting level for spin_lock_irqsave_nested() * it might be natural to create a per-cpu nest count. However, since * we can recurse on ep->poll_wait.lock, and a non-raw spinlock can * schedule() in the -rt kernel, the per-cpu variable are no longer * protected. Thus, we are introducing a per eventpoll nest field. * If we are not being call from ep_poll_callback(), epi is NULL and * we are at the first level of nesting, 0. Otherwise, we are being * called from ep_poll_callback() and if a previous wakeup source is * not an epoll file itself, we are at depth 1 since the wakeup source * is depth 0. If the wakeup source is a previous epoll file in the * wakeup chain then we use its nests value and record ours as * nests + 1. The previous epoll file nests value is stable since its * already holding its own poll_wait.lock. */ if (epi) { if ((is_file_epoll(epi->ffd.file))) { ep_src = epi->ffd.file->private_data; nests = ep_src->nests; } else { nests = 1; } } spin_lock_irqsave_nested(&ep->poll_wait.lock, flags, nests); ep->nests = nests + 1; wake_up_locked_poll(&ep->poll_wait, EPOLLIN | pollflags); ep->nests = 0; spin_unlock_irqrestore(&ep->poll_wait.lock, flags);}
#else
static void ep_poll_safewake(struct eventpoll *ep, struct epitem *epi, __poll_t pollflags){ wake_up_poll(&ep->poll_wait, EPOLLIN | pollflags);}
#endif
static void ep_remove_wait_queue(struct eppoll_entry *pwq){ wait_queue_head_t *whead;
rcu_read_lock(); /* * POLLFREE handshake, acquire side; see "POLLFREE handshake" * at the top of this file. * * A NULL load is paired with the smp_store_release(&whead, NULL) * in ep_poll_callback()'s POLLFREE branch: the teardown is * complete and we must not touch whead again. On a non-NULL load * rcu_read_lock() keeps the waitqueue memory alive (POLLFREE * firers RCU-defer the free) and whead->lock inside * remove_wait_queue() serializes us against the store side. */ whead = smp_load_acquire(&pwq->whead); if (whead) remove_wait_queue(whead, &pwq->wait); rcu_read_unlock();}
/* * This function unregisters poll callbacks from the associated file * descriptor. Must be called with "mtx" held. */static void ep_unregister_pollwait(struct eventpoll *ep, struct epitem *epi){ struct eppoll_entry **p = &epi->pwqlist; struct eppoll_entry *pwq;
while ((pwq = *p) != NULL) { *p = pwq->next; ep_remove_wait_queue(pwq); kmem_cache_free(pwq_cache, pwq); }}
/* call only when ep->mtx is held */static inline struct wakeup_source *ep_wakeup_source(struct epitem *epi){ return rcu_dereference_check(epi->ws, lockdep_is_held(&epi->ep->mtx));}
/* call only when ep->mtx is held */static inline void ep_pm_stay_awake(struct epitem *epi){ struct wakeup_source *ws = ep_wakeup_source(epi);
if (ws) __pm_stay_awake(ws);}
static inline bool ep_has_wakeup_source(struct epitem *epi){ return rcu_access_pointer(epi->ws) ? true : false;}
/* call when ep->mtx cannot be held (ep_poll_callback) */static inline void ep_pm_stay_awake_rcu(struct epitem *epi){ struct wakeup_source *ws;
rcu_read_lock(); ws = rcu_dereference(epi->ws); if (ws) __pm_stay_awake(ws); rcu_read_unlock();}
/* * ep->mutex needs to be held because we could be hit by * eventpoll_release_file() and epoll_ctl(). */static void ep_start_scan(struct eventpoll *ep, struct list_head *scan_batch){ /* * Steal the ready list, and re-init the original one to the * empty list. Also, set ep->ovflist to NULL so that events * happening while looping w/out locks, are not lost. We cannot * have the poll callback to queue directly on ep->rdllist, * because we want the "sproc" callback to be able to do it * in a lockless way. */ lockdep_assert_irqs_enabled(); spin_lock_irq(&ep->lock); write_seqcount_begin(&ep->seq);
list_splice_init(&ep->rdllist, scan_batch); ep_enter_scan(ep);
write_seqcount_end(&ep->seq); spin_unlock_irq(&ep->lock);}
static void ep_done_scan(struct eventpoll *ep, struct list_head *scan_batch){ struct epitem *epi, *nepi;
spin_lock_irq(&ep->lock); /* * During the time we spent inside the "sproc" callback, some * other events might have been queued by the poll callback. * We re-insert them inside the main ready-list here. */ for (nepi = READ_ONCE(ep->ovflist); (epi = nepi) != NULL; ) { nepi = epi->ovflist_next; epi_clear_ovflist(epi); /* * Skip items that the caller already returned via @scan_batch * -- the list_splice() below takes care of those. */ if (!ep_is_linked(epi)) { /* * ovflist is LIFO; list_add() head-insert here * reverses the iteration order into FIFO. */ list_add(&epi->rdllink, &ep->rdllist); ep_pm_stay_awake(epi); } }
write_seqcount_begin(&ep->seq);
/* Back out of scan mode; callbacks target ep->rdllist again. */ ep_exit_scan(ep);
/* * Quickly re-inject items left on "scan_batch". */ list_splice(scan_batch, &ep->rdllist);
write_seqcount_end(&ep->seq);
__pm_relax(ep->ws);
if (!list_empty(&ep->rdllist)) { if (waitqueue_active(&ep->wq)) wake_up(&ep->wq); }
spin_unlock_irq(&ep->lock);}
static void ep_get(struct eventpoll *ep){ refcount_inc(&ep->refcount);}
/* * Drop a reference to @ep; returns true iff it was the last, in which * case the caller is responsible for ep_free(). */static bool ep_put(struct eventpoll *ep){ if (!refcount_dec_and_test(&ep->refcount)) return false;
WARN_ON_ONCE(!RB_EMPTY_ROOT(&ep->rbr.rb_root)); return true;}
static void ep_free(struct eventpoll *ep){ ep_resume_napi_irqs(ep); mutex_destroy(&ep->mtx); free_uid(ep->user); wakeup_source_unregister(ep->ws); /* ep_get_upwards_depth_proc() may still hold epi->ep under RCU */ kfree_rcu(ep, rcu);}
/* * Pin @epi->ffd.file for operations that require both safe dereference * and exclusion from __fput(). * * struct file uses SLAB_TYPESAFE_BY_RCU, so a freed slot can be * reassigned at any time. The bare load of epi->ffd.file is safe here * because the caller holds ep->mtx and eventpoll_release_file() blocks * on that mutex while tearing down the epi, so the backing file * allocation cannot be freed and reused under us. An rcu_read_lock() * is therefore unnecessary for the load. * * A successful file_ref_get() additionally blocks __fput() from * starting on this file: once the refcount has reached zero it cannot * come back. ep_remove() relies on that to touch file->f_lock and * file->f_ep without racing eventpoll_release_file() (see commit * a6dc643c6931). A NULL return means __fput() is already in flight; * the caller must bail without touching the file, and * eventpoll_release_file() will clean the epi up from its side. */static struct file *epi_fget(const struct epitem *epi){ struct file *file;
file = epi->ffd.file; if (!file_ref_get(&file->f_ref)) file = NULL; return file;}
/* * Takes &file->f_lock; returns with it released. */static void ep_remove_file(struct eventpoll *ep, struct epitem *epi, struct file *file){ struct epitems_head *to_free = NULL; struct hlist_head *head;
lockdep_assert_held(&ep->mtx);
spin_lock(&file->f_lock); head = file->f_ep; if (hlist_is_singular_node(&epi->fllink, head)) { /* * Last watcher: publish NULL so the eventpoll_release() * fastpath in include/linux/eventpoll.h can skip the slow * path on a future __fput(). Safe because every f_ep writer * either holds a pin on @file via epi_fget() or is __fput() * itself -- see the comment in eventpoll_release(). */ WRITE_ONCE(file->f_ep, NULL); if (!is_file_epoll(file)) { struct epitems_head *v; v = container_of(head, struct epitems_head, epitems); if (!smp_load_acquire(&v->next)) to_free = v; } } hlist_del_rcu(&epi->fllink); spin_unlock(&file->f_lock); free_ephead(to_free);}
static void ep_remove_epi(struct eventpoll *ep, struct epitem *epi){ lockdep_assert_held(&ep->mtx);
rb_erase_cached(&epi->rbn, &ep->rbr);
spin_lock_irq(&ep->lock); if (ep_is_linked(epi)) list_del_init(&epi->rdllink); spin_unlock_irq(&ep->lock);
wakeup_source_unregister(ep_wakeup_source(epi)); /* * At this point it is safe to free the eventpoll item. Use the union * field epi->rcu, since we are trying to minimize the size of * 'struct epitem'. The 'rbn' field is no longer in use. Protected by * ep->mtx. The rcu read side, reverse_path_check_proc(), does not make * use of the rbn field. */ kfree_rcu(epi, rcu);
percpu_counter_dec(&ep->user->epoll_watches);}
/* * ep_remove variant for callers owing an additional reference to the ep */static void ep_remove(struct eventpoll *ep, struct epitem *epi){ struct file *file __free(fput) = NULL;
lockdep_assert_irqs_enabled(); lockdep_assert_held(&ep->mtx);
ep_unregister_pollwait(ep, epi);
/* * If we manage to grab a reference it means we're not in * eventpoll_release_file() and aren't going to be: once @file's * refcount has reached zero, file_ref_get() cannot bring it back. */ file = epi_fget(epi); if (!file) return;
ep_remove_file(ep, epi, file); ep_remove_epi(ep, epi); WARN_ON_ONCE(ep_put(ep));}
/* * Pass 1 of ep_clear_and_put(): drain every epi's pwqlist. * ep_unregister_pollwait() takes each watched wait-queue head's lock, * which synchronizes with any in-flight ep_poll_callback(); after * this returns no callback can still be about to dereference an epi * on this ep. Must strictly precede ep_drain_tree() -- fusing the * two walks would let a callback queued on epi_i still fire after * epi_{i+k} had already been freed. */static void ep_drain_pollwaits(struct eventpoll *ep){ struct rb_node *rbp; struct epitem *epi;
lockdep_assert_held(&ep->mtx);
for (rbp = rb_first_cached(&ep->rbr); rbp; rbp = rb_next(rbp)) { epi = rb_entry(rbp, struct epitem, rbn);
ep_unregister_pollwait(ep, epi); cond_resched(); }}
/* * Pass 2 of ep_clear_and_put(): ep_remove() every epi. The per-epi * pwqlist is already empty (ep_drain_pollwaits ran), but the rest of * ep_remove() still runs: epi_fget() pin, f_ep clear under f_lock, * rbtree erase, rdllist unlink, kfree_rcu(epi). rb_next() is captured * before each erase so the iteration is stable. * * A concurrent eventpoll_release_file() (removal path C) on a watched * file serializes with us via ep->mtx; ep_remove() transparently * hands off any epi whose file is in __fput() by bailing when * epi_fget() returns NULL, and path C will clean that epi up. */static void ep_drain_tree(struct eventpoll *ep){ struct rb_node *rbp, *next; struct epitem *epi;
lockdep_assert_held(&ep->mtx);
for (rbp = rb_first_cached(&ep->rbr); rbp; rbp = next) { next = rb_next(rbp); epi = rb_entry(rbp, struct epitem, rbn); ep_remove(ep, epi); cond_resched(); }}
/* * Removal path B (see "Removal paths" in the top-of-file banner): * close of the epoll fd itself, reached via ep_eventpoll_release(). * * Two passes under ep->mtx: first ep_drain_pollwaits() quiesces * in-flight callbacks, then ep_drain_tree() frees the epis. The * ep->refcount is kept > 0 across the walk by the ep file's own * share, which we drop below; ep_free() runs iff we were the last * holder after the tree drained. */static void ep_clear_and_put(struct eventpoll *ep){ /* Release any threads blocked in poll-on-ep. */ if (waitqueue_active(&ep->poll_wait)) ep_poll_safewake(ep, NULL, 0);
mutex_lock(&ep->mtx); ep_drain_pollwaits(ep); ep_drain_tree(ep); mutex_unlock(&ep->mtx);
if (ep_put(ep)) ep_free(ep);}
static long ep_eventpoll_ioctl(struct file *file, unsigned int cmd, unsigned long arg){ int ret;
if (!is_file_epoll(file)) return -EINVAL;
switch (cmd) { case EPIOCSPARAMS: case EPIOCGPARAMS: ret = ep_eventpoll_bp_ioctl(file, cmd, arg); break; default: ret = -EINVAL; break; }
return ret;}
static int ep_eventpoll_release(struct inode *inode, struct file *file){ struct eventpoll *ep = file->private_data;
if (ep) ep_clear_and_put(ep);
return 0;}
static __poll_t ep_item_poll(const struct epitem *epi, poll_table *pt, int depth);
static __poll_t __ep_eventpoll_poll(struct file *file, poll_table *wait, int depth){ struct eventpoll *ep = file->private_data; LIST_HEAD(scan_batch); struct epitem *epi, *tmp; poll_table pt; __poll_t res = 0;
init_poll_funcptr(&pt, NULL);
/* Insert inside our poll wait queue */ poll_wait(file, &ep->poll_wait, wait);
/* * Proceed to find out if wanted events are really available inside * the ready list. */ mutex_lock_nested(&ep->mtx, depth); ep_start_scan(ep, &scan_batch); list_for_each_entry_safe(epi, tmp, &scan_batch, rdllink) { if (ep_item_poll(epi, &pt, depth + 1)) { res = EPOLLIN | EPOLLRDNORM; break; } else { /* * Item has been dropped into the ready list by the poll * callback, but it's not actually ready, as far as * caller requested events goes. We can remove it here. */ __pm_relax(ep_wakeup_source(epi)); list_del_init(&epi->rdllink); } } ep_done_scan(ep, &scan_batch); mutex_unlock(&ep->mtx); return res;}
/* * Differs from ep_eventpoll_poll() in that internal callers already have * the ep->mtx so we need to start from depth=1, such that mutex_lock_nested() * is correctly annotated. */static __poll_t ep_item_poll(const struct epitem *epi, poll_table *pt, int depth){ struct file *file = epi_fget(epi); __poll_t res;
/* * We could return EPOLLERR | EPOLLHUP or something, but let's * treat this more as "file doesn't exist, poll didn't happen". */ if (!file) return 0;
pt->_key = epi->event.events; if (!is_file_epoll(file)) res = vfs_poll(file, pt); else res = __ep_eventpoll_poll(file, pt, depth); fput(file); return res & epi->event.events;}
static __poll_t ep_eventpoll_poll(struct file *file, poll_table *wait){ return __ep_eventpoll_poll(file, wait, 0);}
#ifdef CONFIG_PROC_FSstatic void ep_show_fdinfo(struct seq_file *m, struct file *f){ struct eventpoll *ep = f->private_data; struct rb_node *rbp;
mutex_lock(&ep->mtx); for (rbp = rb_first_cached(&ep->rbr); rbp; rbp = rb_next(rbp)) { struct epitem *epi = rb_entry(rbp, struct epitem, rbn); struct inode *inode = file_inode(epi->ffd.file);
seq_printf(m, "tfd: %8d events: %8x data: %16llx " " pos:%lli ino:%llx sdev:%x\n", epi->ffd.fd, epi->event.events, (long long)epi->event.data, (long long)epi->ffd.file->f_pos, inode->i_ino, inode->i_sb->s_dev); if (seq_has_overflowed(m)) break; } mutex_unlock(&ep->mtx);}#endif
/* File callbacks that implement the eventpoll file behaviour */static const struct file_operations eventpoll_fops = {#ifdef CONFIG_PROC_FS .show_fdinfo = ep_show_fdinfo,#endif .release = ep_eventpoll_release, .poll = ep_eventpoll_poll, .llseek = noop_llseek, .unlocked_ioctl = ep_eventpoll_ioctl, .compat_ioctl = compat_ptr_ioctl,};
/* * This is called from eventpoll_release() to unlink files from the eventpoll * interface. We need to have this facility to cleanup correctly files that are * closed without being removed from the eventpoll interface. */void eventpoll_release_file(struct file *file){ struct eventpoll *ep; struct epitem *epi;
/* * A concurrent ep_remove() cannot outrace us: it pins @file via * epi_fget(), which fails once __fput() has dropped the refcount * to zero -- the path we're on. So any racing ep_remove() bails * and leaves the epi for us to clean up here. */again: spin_lock(&file->f_lock); if (file->f_ep && file->f_ep->first) { epi = hlist_entry(file->f_ep->first, struct epitem, fllink); spin_unlock(&file->f_lock);
/* * ep access is safe as we still own a reference to the ep * struct */ ep = epi->ep; mutex_lock(&ep->mtx);
ep_unregister_pollwait(ep, epi);
ep_remove_file(ep, epi, file); ep_remove_epi(ep, epi);
mutex_unlock(&ep->mtx);
if (ep_put(ep)) ep_free(ep); goto again; } spin_unlock(&file->f_lock);}
static int ep_alloc(struct eventpoll **pep){ struct eventpoll *ep;
ep = kzalloc_obj(*ep); if (unlikely(!ep)) return -ENOMEM;
mutex_init(&ep->mtx); spin_lock_init(&ep->lock); seqcount_spinlock_init(&ep->seq, &ep->lock); init_waitqueue_head(&ep->wq); init_waitqueue_head(&ep->poll_wait); INIT_LIST_HEAD(&ep->rdllist); ep->rbr = RB_ROOT_CACHED; ep->ovflist = EP_UNACTIVE_PTR; /* not scanning */ ep->user = get_current_user(); refcount_set(&ep->refcount, 1);
*pep = ep;
return 0;}
/* * Search the file inside the eventpoll tree. The RB tree operations * are protected by the "mtx" mutex, and ep_find() must be called with * "mtx" held. */static struct epitem *ep_find(struct eventpoll *ep, struct epoll_key *tf){ int kcmp; struct rb_node *rbp; struct epitem *epi, *epir = NULL;
for (rbp = ep->rbr.rb_root.rb_node; rbp; ) { epi = rb_entry(rbp, struct epitem, rbn); kcmp = ep_cmp_ffd(tf, &epi->ffd); if (kcmp > 0) rbp = rbp->rb_right; else if (kcmp < 0) rbp = rbp->rb_left; else { epir = epi; break; } }
return epir;}
/* * This is the callback that is passed to the wait queue wakeup * mechanism. It is called by the stored file descriptors when they * have events to report. */static int ep_poll_callback(wait_queue_entry_t *wait, unsigned mode, int sync, void *key){ int pwake = 0; struct epitem *epi = ep_item_from_wait(wait); struct eventpoll *ep = epi->ep; __poll_t pollflags = key_to_poll(key); unsigned long flags; int ewake = 0;
spin_lock_irqsave(&ep->lock, flags);
ep_set_busy_poll_napi_id(epi);
/* * If the event mask does not contain any poll(2) event, we consider the * descriptor to be disabled. This condition is likely the effect of the * EPOLLONESHOT bit that disables the descriptor when an event is received, * until the next EPOLL_CTL_MOD will be issued. */ if (!(epi->event.events & ~EP_PRIVATE_BITS)) goto out_unlock;
/* * Check the events coming with the callback. At this stage, not * every device reports the events in the "key" parameter of the * callback. We need to be able to handle both cases here, hence the * test for "key" != NULL before the event match test. */ if (pollflags && !(pollflags & epi->event.events)) goto out_unlock;
/* * If we are transferring events to userspace, we can hold no locks * (because we're accessing user memory, and because of linux f_op->poll() * semantics). All the events that happen during that period of time are * chained in ep->ovflist and requeued later on. */ if (ep_is_scanning(ep)) { if (!epi_on_ovflist(epi)) { epi->ovflist_next = READ_ONCE(ep->ovflist); WRITE_ONCE(ep->ovflist, epi); ep_pm_stay_awake_rcu(epi); } } else if (!ep_is_linked(epi)) { /* In the usual case, add event to ready list. */ list_add_tail(&epi->rdllink, &ep->rdllist); ep_pm_stay_awake_rcu(epi); }
/* * Wake up ( if active ) both the eventpoll wait list and the ->poll() * wait list. */ if (waitqueue_active(&ep->wq)) { if ((epi->event.events & EPOLLEXCLUSIVE) && !(pollflags & POLLFREE)) { switch (pollflags & EPOLLINOUT_BITS) { case EPOLLIN: if (epi->event.events & EPOLLIN) ewake = 1; break; case EPOLLOUT: if (epi->event.events & EPOLLOUT) ewake = 1; break; case 0: ewake = 1; break; } } if (sync) wake_up_sync(&ep->wq); else wake_up(&ep->wq); } if (waitqueue_active(&ep->poll_wait)) pwake++;
out_unlock: spin_unlock_irqrestore(&ep->lock, flags);
/* We have to call this outside the lock */ if (pwake) ep_poll_safewake(ep, epi, pollflags & EPOLL_URING_WAKE);
if (!(epi->event.events & EPOLLEXCLUSIVE)) ewake = 1;
if (pollflags & POLLFREE) { /* * POLLFREE handshake, release side; see "POLLFREE handshake" * at the top of this file. * * Unlink our wait entry with list_del_init rather than * __remove_wait_queue: a concurrent ep_remove_wait_queue() * that already loaded a non-NULL whead may still call * remove_wait_queue() after us, and list_del_init() tolerates * the second delete. * * smp_store_release(&whead, NULL) publishes the teardown to * ep_remove_wait_queue()'s smp_load_acquire(). Before this * store, a racing ep_clear_and_put() / ep_remove() reaches * ep_remove_wait_queue() which sees whead != NULL and takes * whead->lock -- the same lock held by our caller, so it * serializes behind us. Once whead is zeroed, nothing else * protects ep / epi / wait. */ list_del_init(&wait->entry); smp_store_release(&ep_pwq_from_wait(wait)->whead, NULL); }
return ewake;}
/* * This is the callback that is used to add our wait queue to the * target file wakeup lists. */static void ep_ptable_queue_proc(struct file *file, wait_queue_head_t *whead, poll_table *pt){ struct ep_pqueue *epq = container_of(pt, struct ep_pqueue, pt); struct epitem *epi = epq->epi; struct eppoll_entry *pwq;
if (unlikely(!epi)) // an earlier allocation has failed return;
pwq = kmem_cache_alloc(pwq_cache, GFP_KERNEL); if (unlikely(!pwq)) { epq->epi = NULL; return; }
init_waitqueue_func_entry(&pwq->wait, ep_poll_callback); pwq->whead = whead; pwq->base = epi; if (epi->event.events & EPOLLEXCLUSIVE) add_wait_queue_exclusive(whead, &pwq->wait); else add_wait_queue(whead, &pwq->wait); pwq->next = epi->pwqlist; epi->pwqlist = pwq;}
static void ep_rbtree_insert(struct eventpoll *ep, struct epitem *epi){ int kcmp; struct rb_node **p = &ep->rbr.rb_root.rb_node, *parent = NULL; struct epitem *epic; bool leftmost = true;
while (*p) { parent = *p; epic = rb_entry(parent, struct epitem, rbn); kcmp = ep_cmp_ffd(&epi->ffd, &epic->ffd); if (kcmp > 0) { p = &parent->rb_right; leftmost = false; } else p = &parent->rb_left; } rb_link_node(&epi->rbn, parent, p); rb_insert_color_cached(&epi->rbn, &ep->rbr, leftmost);}
/* * Upper bound on wakeup paths emanating from any one watched file, * indexed by path depth (1..PATH_ARR_SIZE). For example, we allow * 1000 paths of length 1 from each watched file. These caps limit * the wakeup amplification that can be built from epoll-watches- * epoll topologies without rejecting reasonable usage. * * Enforced at EPOLL_CTL_ADD; CTL_MOD and CTL_DEL cannot add paths. * The running tallies live in ctx->path_count[] and are protected by * epnested_mutex. */static const int path_limits[PATH_ARR_SIZE] = { 1000, 500, 100, 50, 10 };
static int path_count_inc(struct ep_ctl_ctx *ctx, int nests){ /* Allow an arbitrary number of depth 1 paths */ if (nests == 0) return 0;
if (++ctx->path_count[nests] > path_limits[nests]) return -1; return 0;}
static void path_count_init(struct ep_ctl_ctx *ctx){ int i;
for (i = 0; i < PATH_ARR_SIZE; i++) ctx->path_count[i] = 0;}
static int reverse_path_check_proc(struct ep_ctl_ctx *ctx, struct hlist_head *refs, int depth){ int error = 0; struct epitem *epi;
if (depth > EP_MAX_NESTS) /* too deep nesting */ return -1;
/* CTL_DEL can remove links here, but that can't increase our count */ hlist_for_each_entry_rcu(epi, refs, fllink) { struct hlist_head *refs = &epi->ep->refs; if (hlist_empty(refs)) error = path_count_inc(ctx, depth); else error = reverse_path_check_proc(ctx, refs, depth + 1); if (error != 0) break; } return error;}
/** * reverse_path_check - ctx->tfile_check_list is a list of epitems_head * anchoring files with newly proposed links; make * sure those links don't push any path-length bucket * over its limit in path_limits[]. * @ctx: Per-do_epoll_ctl() scratch for the loop / path checks. * * Return: %zero if the proposed links don't create too many paths, * %-1 otherwise. */static int reverse_path_check(struct ep_ctl_ctx *ctx){ struct epitems_head *p;
for (p = ctx->tfile_check_list; p != EP_UNACTIVE_PTR; p = p->next) { int error; path_count_init(ctx); rcu_read_lock(); error = reverse_path_check_proc(ctx, &p->epitems, 0); rcu_read_unlock(); if (error) return error; } return 0;}
static int ep_create_wakeup_source(struct epitem *epi){ struct name_snapshot n; struct wakeup_source *ws;
if (!epi->ep->ws) { epi->ep->ws = wakeup_source_register(NULL, "eventpoll"); if (!epi->ep->ws) return -ENOMEM; }
take_dentry_name_snapshot(&n, epi->ffd.file->f_path.dentry); ws = wakeup_source_register(NULL, n.name.name); release_dentry_name_snapshot(&n);
if (!ws) return -ENOMEM; rcu_assign_pointer(epi->ws, ws);
return 0;}
/* rare code path, only used when EPOLL_CTL_MOD removes a wakeup source */static noinline void ep_destroy_wakeup_source(struct epitem *epi){ struct wakeup_source *ws = ep_wakeup_source(epi);
RCU_INIT_POINTER(epi->ws, NULL);
/* * wait for ep_pm_stay_awake_rcu to finish, synchronize_rcu is * used internally by wakeup_source_remove, too (called by * wakeup_source_unregister), so we cannot use call_rcu */ synchronize_rcu(); wakeup_source_unregister(ws);}
static int ep_attach_file(struct file *file, struct epitem *epi){ struct epitems_head *to_free = NULL; struct hlist_head *head = NULL; struct eventpoll *ep = NULL;
if (is_file_epoll(file)) ep = file->private_data;
if (ep) { head = &ep->refs; } else if (!READ_ONCE(file->f_ep)) {allocate: to_free = kmem_cache_zalloc(ephead_cache, GFP_KERNEL); if (!to_free) return -ENOMEM; head = &to_free->epitems; } spin_lock(&file->f_lock); if (!file->f_ep) { if (unlikely(!head)) { spin_unlock(&file->f_lock); goto allocate; } /* See eventpoll_release() for details. */ WRITE_ONCE(file->f_ep, head); to_free = NULL; } hlist_add_head_rcu(&epi->fllink, file->f_ep); spin_unlock(&file->f_lock); free_ephead(to_free); return 0;}
/* * Charge the user's epoll_watches quota, allocate a fresh epitem for * @tf, and initialize its fields. The returned item is not yet linked * into any data structure; the caller must install it via * ep_register_epitem() (which takes over on success) or kmem_cache_free() * it and decrement epoll_watches on its own. * * Returns ERR_PTR(-ENOSPC) if the quota is exceeded, ERR_PTR(-ENOMEM) * if the slab allocation fails. */static struct epitem *ep_alloc_epitem(struct eventpoll *ep, const struct epoll_event *event, struct epoll_key *tf){ struct epitem *epi;
if (unlikely(percpu_counter_compare(&ep->user->epoll_watches, max_user_watches) >= 0)) return ERR_PTR(-ENOSPC); percpu_counter_inc(&ep->user->epoll_watches);
epi = kmem_cache_zalloc(epi_cache, GFP_KERNEL); if (unlikely(!epi)) { percpu_counter_dec(&ep->user->epoll_watches); return ERR_PTR(-ENOMEM); }
INIT_LIST_HEAD(&epi->rdllink); epi->ep = ep; epi->ffd = *tf; epi->event = *event; epi_clear_ovflist(epi);
return epi;}
/* * Install @epi into its target file's f_ep hlist and into @ep's rbtree, * taking one additional reference on @ep for the lifetime of the item. * * If @tep is non-NULL, the target file is itself an eventpoll; we hold * tep->mtx at subclass 1 across the attach + rbtree insert to serialize * with the target side. RB tree ops are protected by @ep->mtx, which * the caller already holds. * * On failure the epi is freed and the epoll_watches counter decremented, * matching ep_alloc_epitem()'s allocation. After this returns * successfully, ep_insert()'s later error paths use ep_remove() for * unwind; that cannot drop @ep's refcount to zero because the ep file * itself still holds the original reference. */static int ep_register_epitem(struct ep_ctl_ctx *ctx, struct eventpoll *ep, struct epitem *epi, struct eventpoll *tep, int full_check){ struct file *tfile = epi->ffd.file; int error;
if (tep) mutex_lock_nested(&tep->mtx, 1);
error = ep_attach_file(tfile, epi); if (unlikely(error)) { if (tep) mutex_unlock(&tep->mtx); kmem_cache_free(epi_cache, epi); percpu_counter_dec(&ep->user->epoll_watches); return error; }
if (full_check && !tep) list_file(tfile, ctx);
ep_rbtree_insert(ep, epi);
if (tep) mutex_unlock(&tep->mtx);
ep_get(ep); return 0;}
/* * Must be called with "mtx" held. */static int ep_insert(struct ep_ctl_ctx *ctx, struct eventpoll *ep, const struct epoll_event *event, struct epoll_key *tf, int full_check){ int error, pwake = 0; __poll_t revents; struct epitem *epi; struct ep_pqueue epq; struct eventpoll *tep = NULL;
if (is_file_epoll(tf->file)) tep = tf->file->private_data;
lockdep_assert_irqs_enabled();
epi = ep_alloc_epitem(ep, event, tf); if (IS_ERR(epi)) return PTR_ERR(epi);
error = ep_register_epitem(ctx, ep, epi, tep, full_check); if (error) return error;
/* Reject the insert if the new link would create too many back-paths. */ if (unlikely(full_check && reverse_path_check(ctx))) { ep_remove(ep, epi); return -EINVAL; }
if (epi->event.events & EPOLLWAKEUP) { error = ep_create_wakeup_source(epi); if (error) { ep_remove(ep, epi); return error; } }
/* Initialize the poll table using the queue callback */ epq.epi = epi; init_poll_funcptr(&epq.pt, ep_ptable_queue_proc);
/* * Attach the item to the poll hooks and get current event bits. * We can safely use the file* here because its usage count has * been increased by the caller of this function. Note that after * this operation completes, the poll callback can start hitting * the new item. */ revents = ep_item_poll(epi, &epq.pt, 1);
/* ep_ptable_queue_proc() signals allocation failure by clearing epq.epi. */ if (unlikely(!epq.epi)) { ep_remove(ep, epi); return -ENOMEM; }
/* Drop the new item onto the ready list if it is already ready. */ spin_lock_irq(&ep->lock);
ep_set_busy_poll_napi_id(epi);
if (revents && !ep_is_linked(epi)) { list_add_tail(&epi->rdllink, &ep->rdllist); ep_pm_stay_awake(epi);
if (waitqueue_active(&ep->wq)) wake_up(&ep->wq); if (waitqueue_active(&ep->poll_wait)) pwake++; }
spin_unlock_irq(&ep->lock);
/* We have to call this outside the lock */ if (pwake) ep_poll_safewake(ep, NULL, 0);
return 0;}
/* * Modify the interest event mask by dropping an event if the new mask * has a match in the current file status. Must be called with "mtx" held. */static int ep_modify(struct eventpoll *ep, struct epitem *epi, const struct epoll_event *event){ int pwake = 0; poll_table pt;
lockdep_assert_irqs_enabled();
init_poll_funcptr(&pt, NULL);
/* * Set the new event interest mask before calling f_op->poll(); * otherwise we might miss an event that happens between the * f_op->poll() call and the new event set registering. */ epi->event.events = event->events; /* need barrier below */ epi->event.data = event->data; /* protected by mtx */ if (epi->event.events & EPOLLWAKEUP) { if (!ep_has_wakeup_source(epi)) ep_create_wakeup_source(epi); } else if (ep_has_wakeup_source(epi)) { ep_destroy_wakeup_source(epi); }
/* * The following barrier has two effects: * * 1) Flush epi changes above to other CPUs. This ensures * we do not miss events from ep_poll_callback if an * event occurs immediately after we call f_op->poll(). * We need this because we did not take ep->lock while * changing epi above (but ep_poll_callback does take * ep->lock). * * 2) We also need to ensure we do not miss _past_ events * when calling f_op->poll(). This barrier also * pairs with the barrier in wq_has_sleeper (see * comments for wq_has_sleeper). * * This barrier will now guarantee ep_poll_callback or f_op->poll * (or both) will notice the readiness of an item. */ smp_mb();
/* * Get current event bits. We can safely use the file* here because * its usage count has been increased by the caller of this function. * If the item is "hot" and it is not registered inside the ready * list, push it inside. */ if (ep_item_poll(epi, &pt, 1)) { spin_lock_irq(&ep->lock); if (!ep_is_linked(epi)) { list_add_tail(&epi->rdllink, &ep->rdllist); ep_pm_stay_awake(epi);
/* Notify waiting tasks that events are available */ if (waitqueue_active(&ep->wq)) wake_up(&ep->wq); if (waitqueue_active(&ep->poll_wait)) pwake++; } spin_unlock_irq(&ep->lock); }
/* We have to call this outside the lock */ if (pwake) ep_poll_safewake(ep, NULL, 0);
return 0;}
/* * Attempt to deliver one event for @epi into @*uevents. * * Returns 1 if an event was delivered (with *uevents advanced to the * next slot), 0 if the re-poll reported no caller-requested events * (@epi drops out of the ready list; a future callback will re-add * it), or -EFAULT if copy_to_user() faulted (in which case @epi is * re-inserted at the head of @scan_batch so ep_done_scan() merges it * back to rdllist for the next attempt). * * PM bookkeeping and level-triggered re-queue are handled here. * Caller holds ep->mtx and the scan is active. */static int ep_deliver_event(struct eventpoll *ep, struct epitem *epi, poll_table *pt, struct epoll_event __user **uevents, struct list_head *scan_batch){ struct epoll_event __user *next; struct wakeup_source *ws; __poll_t revents;
/* * Activate ep->ws before deactivating epi->ws to prevent * triggering auto-suspend here (in case we reactivate epi->ws * below). Rearranging to delay the deactivation would let * epi->ws drift out of sync with ep_is_linked(). */ ws = ep_wakeup_source(epi); if (ws) { if (ws->active) __pm_stay_awake(ep->ws); __pm_relax(ws); }
list_del_init(&epi->rdllink);
/* * Re-poll under ep->mtx so userspace cannot change the item * out from under us. If no caller-requested events remain, * @epi stays off the ready list; the poll callback will * re-queue it when events next appear. */ revents = ep_item_poll(epi, pt, 1); if (!revents) return 0;
next = epoll_put_uevent(revents, epi->event.data, *uevents); if (!next) { /* * copy_to_user() faulted: put the item back so * ep_done_scan() splices it onto rdllist for the next * attempt. */ list_add(&epi->rdllink, scan_batch); ep_pm_stay_awake(epi); return -EFAULT; } *uevents = next;
if (epi->event.events & EPOLLONESHOT) { epi->event.events &= EP_PRIVATE_BITS; } else if (!(epi->event.events & EPOLLET)) { /* * Level-triggered: re-queue so the next epoll_wait() * rechecks availability. We are the sole writer to * rdllist here -- epoll_ctl() callers are locked out * by ep->mtx, and the poll callback queues to ovflist * during scans. */ list_add_tail(&epi->rdllink, &ep->rdllist); ep_pm_stay_awake(epi); } return 1;}
static int ep_send_events(struct eventpoll *ep, struct epoll_event __user *events, int maxevents){ struct epitem *epi, *tmp; LIST_HEAD(scan_batch); poll_table pt; int res = 0;
/* * Always short-circuit for fatal signals to allow threads to make a * timely exit without the chance of finding more events available and * fetching repeatedly. */ if (fatal_signal_pending(current)) return -EINTR;
init_poll_funcptr(&pt, NULL);
mutex_lock(&ep->mtx); ep_start_scan(ep, &scan_batch);
/* * We can loop without lock because we are passed a task-private * scan_batch; items cannot vanish while we hold ep->mtx. */ list_for_each_entry_safe(epi, tmp, &scan_batch, rdllink) { int delivered;
if (res >= maxevents) break;
delivered = ep_deliver_event(ep, epi, &pt, &events, &scan_batch); if (delivered < 0) { if (!res) res = delivered; break; } res += delivered; }
ep_done_scan(ep, &scan_batch); mutex_unlock(&ep->mtx);
return res;}
static struct timespec64 *ep_timeout_to_timespec(struct timespec64 *to, long ms){ struct timespec64 now;
if (ms < 0) return NULL;
if (!ms) { to->tv_sec = 0; to->tv_nsec = 0; return to; }
to->tv_sec = ms / MSEC_PER_SEC; to->tv_nsec = NSEC_PER_MSEC * (ms % MSEC_PER_SEC);
ktime_get_ts64(&now); *to = timespec64_add_safe(now, *to); return to;}
/* * autoremove_wake_function, but remove even on failure to wake up, because we * know that default_wake_function/ttwu will only fail if the thread is already * woken, and in that case the ep_poll loop will remove the entry anyways, not * try to reuse it. */static int ep_autoremove_wake_function(struct wait_queue_entry *wq_entry, unsigned int mode, int sync, void *key){ int ret = default_wake_function(wq_entry, mode, sync, key);
/* * Pairs with list_empty_careful in ep_poll, and ensures future loop * iterations see the cause of this wakeup. */ list_del_init_careful(&wq_entry->entry); return ret;}
static int ep_try_send_events(struct eventpoll *ep, struct epoll_event __user *events, int maxevents){ int res;
/* * Try to transfer events to user space. In case we get 0 events and * there's still timeout left over, we go trying again in search of * more luck. */ res = ep_send_events(ep, events, maxevents); if (res > 0) ep_suspend_napi_irqs(ep); return res;}
static int ep_schedule_timeout(ktime_t *to){ if (to) return ktime_after(*to, ktime_get()); else return 1;}
/** * ep_poll - Retrieves ready events, and delivers them to the caller-supplied * event buffer. * * @ep: Pointer to the eventpoll context. * @events: Pointer to the userspace buffer where the ready events should be * stored. * @maxevents: Size (in terms of number of events) of the caller event buffer. * @timeout: Maximum timeout for the ready events fetch operation, in * timespec. If the timeout is zero, the function will not block, * while if the @timeout ptr is NULL, the function will block * until at least one event has been retrieved (or an error * occurred). * * Return: the number of ready events which have been fetched, or an * error code, in case of error. */static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events, int maxevents, struct timespec64 *timeout){ int res, timed_out = 0; bool eavail; u64 slack = 0; wait_queue_entry_t wait; ktime_t expires, *to = NULL;
lockdep_assert_irqs_enabled();
if (timeout && (timeout->tv_sec | timeout->tv_nsec)) { slack = select_estimate_accuracy(timeout); to = &expires; *to = timespec64_to_ktime(*timeout); } else if (timeout) { /* * Avoid the unnecessary trip to the wait queue loop, if the * caller specified a non blocking operation. */ timed_out = 1; }
/* * This call is racy: We may or may not see events that are being added * to the ready list under the lock (e.g., in IRQ callbacks). For cases * with a non-zero timeout, this thread will check the ready list under * lock and will add to the wait queue. For cases with a zero * timeout, the user by definition should not care and will have to * recheck again. */ eavail = ep_events_available(ep);
while (1) { if (eavail) { res = ep_try_send_events(ep, events, maxevents); if (res) return res; }
if (timed_out) return 0;
eavail = ep_busy_loop(ep); if (eavail) continue;
if (signal_pending(current)) return -EINTR;
/* * Internally init_wait() uses autoremove_wake_function(), * thus wait entry is removed from the wait queue on each * wakeup. Why it is important? In case of several waiters * each new wakeup will hit the next waiter, giving it the * chance to harvest new event. Otherwise wakeup can be * lost. This is also good performance-wise, because on * normal wakeup path no need to call __remove_wait_queue() * explicitly, thus ep->lock is not taken, which halts the * event delivery. * * In fact, we now use an even more aggressive function that * unconditionally removes, because we don't reuse the wait * entry between loop iterations. This lets us also avoid the * performance issue if a process is killed, causing all of its * threads to wake up without being removed normally. */ init_wait(&wait); wait.func = ep_autoremove_wake_function;
spin_lock_irq(&ep->lock); /* * Barrierless variant, waitqueue_active() is called under * the same lock on wakeup ep_poll_callback() side, so it * is safe to avoid an explicit barrier. */ __set_current_state(TASK_INTERRUPTIBLE);
/* * Do the final check under the lock. ep_start/done_scan() * plays with two lists (->rdllist and ->ovflist) and there * is always a race when both lists are empty for short * period of time although events are pending, so lock is * important. */ eavail = ep_events_available(ep); if (!eavail) __add_wait_queue_exclusive(&ep->wq, &wait);
spin_unlock_irq(&ep->lock);
if (!eavail) timed_out = !ep_schedule_timeout(to) || !schedule_hrtimeout_range(to, slack, HRTIMER_MODE_ABS); __set_current_state(TASK_RUNNING);
/* * We were woken up, thus go and try to harvest some events. * If timed out and still on the wait queue, recheck eavail * carefully under lock, below. */ eavail = true;
if (!list_empty_careful(&wait.entry)) { spin_lock_irq(&ep->lock); /* * If the thread timed out and is not on the wait queue, * it means that the thread was woken up after its * timeout expired before it could reacquire the lock. * Thus, when wait.entry is empty, it needs to harvest * events. */ if (timed_out) eavail = list_empty(&wait.entry); __remove_wait_queue(&ep->wq, &wait); spin_unlock_irq(&ep->lock); } }}
/** * ep_loop_check_proc - verify that adding an epoll file @ep inside another * epoll file does not create closed loops, and * determine the depth of the subtree starting at @ep * * @ctx: Per-do_epoll_ctl() scratch for the loop / path checks. * @ep: the &struct eventpoll to be currently checked. * @depth: Current depth of the path being checked. * * Return: depth of the subtree, or a value bigger than EP_MAX_NESTS if we found * a loop or went too deep. */static int ep_loop_check_proc(struct ep_ctl_ctx *ctx, struct eventpoll *ep, int depth){ int result = 0; struct rb_node *rbp; struct epitem *epi;
if (ep->gen == loop_check_gen) return ep->loop_check_depth;
mutex_lock_nested(&ep->mtx, depth + 1); ep->gen = loop_check_gen; for (rbp = rb_first_cached(&ep->rbr); rbp; rbp = rb_next(rbp)) { epi = rb_entry(rbp, struct epitem, rbn); if (unlikely(is_file_epoll(epi->ffd.file))) { struct eventpoll *ep_tovisit; ep_tovisit = epi->ffd.file->private_data; if (ep_tovisit == ctx->inserting_into || depth > EP_MAX_NESTS) result = EP_MAX_NESTS+1; else result = max(result, ep_loop_check_proc(ctx, ep_tovisit, depth + 1) + 1); if (result > EP_MAX_NESTS) break; } else { /* * A non-epoll leaf. Queue it for the companion * reverse_path_check() that runs after this walk so * any new links we propose don't add too many wakeup * paths. */ list_file(epi->ffd.file, ctx); } } ep->loop_check_depth = result; mutex_unlock(&ep->mtx);
return result;}
/* ep_get_upwards_depth_proc - determine depth of @ep when traversed upwards */static int ep_get_upwards_depth_proc(struct eventpoll *ep, int depth){ int result = 0; struct epitem *epi;
if (ep->gen == loop_check_gen) return ep->loop_check_depth; hlist_for_each_entry_rcu(epi, &ep->refs, fllink) result = max(result, ep_get_upwards_depth_proc(epi->ep, depth + 1) + 1); ep->gen = loop_check_gen; ep->loop_check_depth = result; return result;}
/** * ep_loop_check - Performs a check to verify that adding an epoll file (@to) * into another epoll file (represented by @ep) does not create * closed loops or too deep chains. * * @ctx: Per-CTL_ADD scratch context. * @ep: Pointer to the epoll we are inserting into. * @to: Pointer to the epoll to be inserted. * * Return: %zero if adding the epoll @to inside the epoll @from * does not violate the constraints, or %-1 otherwise. */static int ep_loop_check(struct ep_ctl_ctx *ctx, struct eventpoll *ep, struct eventpoll *to){ int depth, upwards_depth;
ctx->inserting_into = ep; /* * Check how deep down we can get from @to, and whether it is possible * to loop up to @ep. */ depth = ep_loop_check_proc(ctx, to, 0); if (depth > EP_MAX_NESTS) return -1; /* Check how far up we can go from @ep. */ rcu_read_lock(); upwards_depth = ep_get_upwards_depth_proc(ep, 0); rcu_read_unlock();
return (depth+1+upwards_depth > EP_MAX_NESTS) ? -1 : 0;}
static void clear_tfile_check_list(struct ep_ctl_ctx *ctx){ rcu_read_lock(); while (ctx->tfile_check_list != EP_UNACTIVE_PTR) { struct epitems_head *head = ctx->tfile_check_list; ctx->tfile_check_list = head->next; unlist_file(head); } rcu_read_unlock();}
/* * Open an eventpoll file descriptor. */static int do_epoll_create(int flags){ int error; struct eventpoll *ep;
/* Check the EPOLL_* constant for consistency. */ BUILD_BUG_ON(EPOLL_CLOEXEC != O_CLOEXEC);
if (flags & ~EPOLL_CLOEXEC) return -EINVAL; /* * Create the internal data structure ("struct eventpoll"). */ error = ep_alloc(&ep); if (error < 0) return error; /* * Creates all the items needed to setup an eventpoll file. That is, * a file structure and a free file descriptor. */ FD_PREPARE(fdf, O_RDWR | (flags & O_CLOEXEC), anon_inode_getfile("[eventpoll]", &eventpoll_fops, ep, O_RDWR | (flags & O_CLOEXEC))); if (fdf.err) { ep_clear_and_put(ep); return fdf.err; } ep->file = fd_prepare_file(fdf); return fd_publish(fdf);}
SYSCALL_DEFINE1(epoll_create1, int, flags){ return do_epoll_create(flags);}
SYSCALL_DEFINE1(epoll_create, int, size){ if (size <= 0) return -EINVAL;
return do_epoll_create(0);}
#ifdef CONFIG_PM_SLEEPstatic inline void ep_take_care_of_epollwakeup(struct epoll_event *epev){ if ((epev->events & EPOLLWAKEUP) && !capable(CAP_BLOCK_SUSPEND)) epev->events &= ~EPOLLWAKEUP;}#elsestatic inline void ep_take_care_of_epollwakeup(struct epoll_event *epev){ epev->events &= ~EPOLLWAKEUP;}#endif
static inline int epoll_mutex_lock(struct mutex *mutex, bool nonblock){ if (!nonblock) { mutex_lock(mutex); return 0; } return mutex_trylock(mutex) ? 0 : -EAGAIN;}
/* * Acquire the locks required for do_epoll_ctl() on @ep for @op. * * Always takes ep->mtx. For EPOLL_CTL_ADD, additionally runs the * loop / path check under epnested_mutex when the topology can * change: @ep is already watched (epfile->f_ep non-NULL), @ep was * recently loop-checked (ep->gen == loop_check_gen), or @tfile is * itself an eventpoll. * * Return value encodes both outcome and lock state: * * 0 success; ep->mtx held. * 1 success; ep->mtx held AND the full check ran under * epnested_mutex (which is also still held). The value * doubles as the @full_check argument to ep_insert(). * -errno failure; no locks held. * * The caller releases what was taken with ep_ctl_unlock(ep, ret). * * Holding epnested_mutex on add is what prevents two racing * EPOLL_CTL_ADDs on different eps from building a cycle without * either walker observing it. */static int ep_ctl_lock(struct ep_ctl_ctx *ctx, struct eventpoll *ep, int op, struct file *epfile, struct file *tfile, bool nonblock){ struct eventpoll *tep; int error;
error = epoll_mutex_lock(&ep->mtx, nonblock); if (error) return error;
if (op != EPOLL_CTL_ADD) return 0; if (!READ_ONCE(epfile->f_ep) && ep->gen != loop_check_gen && !is_file_epoll(tfile)) return 0;
/* Full check needed: drop ep->mtx so we can take epnested_mutex. */ mutex_unlock(&ep->mtx); error = epoll_mutex_lock(&epnested_mutex, nonblock); if (error) return error;
loop_check_gen++;
if (is_file_epoll(tfile)) { tep = tfile->private_data; if (ep_loop_check(ctx, ep, tep) != 0) { error = -ELOOP; goto err_unlock_nested; } }
error = epoll_mutex_lock(&ep->mtx, nonblock); if (error) goto err_unlock_nested;
return 1;
err_unlock_nested: clear_tfile_check_list(ctx); loop_check_gen++; mutex_unlock(&epnested_mutex); return error;}
static void ep_ctl_unlock(struct ep_ctl_ctx *ctx, struct eventpoll *ep, int full_check){ mutex_unlock(&ep->mtx); if (full_check) { clear_tfile_check_list(ctx); loop_check_gen++; mutex_unlock(&epnested_mutex); }}
int do_epoll_ctl_file(struct file *f, int op, struct epoll_key *tf, struct epoll_event *epds, bool nonblock){ int error; int full_check; struct eventpoll *ep; struct epitem *epi; struct ep_ctl_ctx ctx = { .tfile_check_list = EP_UNACTIVE_PTR, };
/* The target file descriptor must support poll */ if (!file_can_poll(tf->file)) return -EPERM;
/* Check if EPOLLWAKEUP is allowed */ if (ep_op_has_event(op)) ep_take_care_of_epollwakeup(epds);
/* * The @f file must itself be an eventpoll, and we do not permit * adding an epoll file descriptor inside itself. */ if (f == tf->file || !is_file_epoll(f)) return -EINVAL;
/* * epoll adds to the wakeup queue at EPOLL_CTL_ADD time only, * so EPOLLEXCLUSIVE is not allowed for a EPOLL_CTL_MOD operation. * Also, nested exclusive wakeups are not supported. */ if (ep_op_has_event(op) && (epds->events & EPOLLEXCLUSIVE)) { if (op == EPOLL_CTL_MOD) return -EINVAL; if (op == EPOLL_CTL_ADD && (is_file_epoll(tf->file) || (epds->events & ~EPOLLEXCLUSIVE_OK_BITS))) return -EINVAL; }
ep = f->private_data;
full_check = ep_ctl_lock(&ctx, ep, op, f, tf->file, nonblock); if (full_check < 0) return full_check;
/* * Look the target up in ep's RB tree. We hold ep->mtx, so the * item stays valid until we release. */ epi = ep_find(ep, tf);
error = -EINVAL; switch (op) { case EPOLL_CTL_ADD: if (!epi) { epds->events |= EPOLLERR | EPOLLHUP; error = ep_insert(&ctx, ep, epds, tf, full_check); } else error = -EEXIST; break; case EPOLL_CTL_DEL: if (epi) { /* * The eventpoll itself is still alive: the refcount * can't go to zero here. */ ep_remove(ep, epi); error = 0; } else { error = -ENOENT; } break; case EPOLL_CTL_MOD: if (epi) { if (!(epi->event.events & EPOLLEXCLUSIVE)) { epds->events |= EPOLLERR | EPOLLHUP; error = ep_modify(ep, epi, epds); } } else error = -ENOENT; break; }
ep_ctl_unlock(&ctx, ep, full_check); return error;}
int do_epoll_ctl(int epfd, int op, int fd, struct epoll_event *epds, bool nonblock){ struct epoll_key efd;
CLASS(fd, f)(epfd); if (fd_empty(f)) return -EBADF;
/* Get the "struct file *" for the target file */ CLASS(fd, tf)(fd); if (fd_empty(tf)) return -EBADF;
efd.file = fd_file(tf); efd.fd = fd; return do_epoll_ctl_file(fd_file(f), op, &efd, epds, nonblock);}
/* * The following function implements the controller interface for * the eventpoll file that enables the insertion/removal/change of * file descriptors inside the interest set. */SYSCALL_DEFINE4(epoll_ctl, int, epfd, int, op, int, fd, struct epoll_event __user *, event){ struct epoll_event epds;
if (ep_op_has_event(op) && copy_from_user(&epds, event, sizeof(struct epoll_event))) return -EFAULT;
return do_epoll_ctl(epfd, op, fd, &epds, false);}
static int ep_check_params(struct file *file, struct epoll_event __user *evs, int maxevents){ /* The maximum number of event must be greater than zero */ if (maxevents <= 0 || maxevents > EP_MAX_EVENTS) return -EINVAL;
/* Verify that the area passed by the user is writeable */ if (!access_ok(evs, maxevents * sizeof(struct epoll_event))) return -EFAULT;
/* * We have to check that the file structure underneath the fd * the user passed to us _is_ an eventpoll file. */ if (!is_file_epoll(file)) return -EINVAL;
return 0;}
int epoll_sendevents(struct file *file, struct epoll_event __user *events, int maxevents){ struct eventpoll *ep; int ret;
ret = ep_check_params(file, events, maxevents); if (unlikely(ret)) return ret;
ep = file->private_data; /* * Racy call, but that's ok - it should get retried based on * poll readiness anyway. */ if (ep_events_available(ep)) return ep_try_send_events(ep, events, maxevents); return 0;}
/* * Implement the event wait interface for the eventpoll file. It is the kernel * part of the user space epoll_wait(2). */static int do_epoll_wait(int epfd, struct epoll_event __user *events, int maxevents, struct timespec64 *to){ struct eventpoll *ep; int ret;
/* Get the "struct file *" for the eventpoll file */ CLASS(fd, f)(epfd); if (fd_empty(f)) return -EBADF;
ret = ep_check_params(fd_file(f), events, maxevents); if (unlikely(ret)) return ret;
/* * At this point it is safe to assume that the "private_data" contains * our own data structure. */ ep = fd_file(f)->private_data;
/* Time to fish for events ... */ return ep_poll(ep, events, maxevents, to);}
SYSCALL_DEFINE4(epoll_wait, int, epfd, struct epoll_event __user *, events, int, maxevents, int, timeout){ struct timespec64 to;
return do_epoll_wait(epfd, events, maxevents, ep_timeout_to_timespec(&to, timeout));}
/* * Implement the event wait interface for the eventpoll file. It is the kernel * part of the user space epoll_pwait(2). */static int do_epoll_pwait(int epfd, struct epoll_event __user *events, int maxevents, struct timespec64 *to, const sigset_t __user *sigmask, size_t sigsetsize){ int error;
/* * If the caller wants a certain signal mask to be set during the wait, * we apply it here. */ error = set_user_sigmask(sigmask, sigsetsize); if (error) return error;
error = do_epoll_wait(epfd, events, maxevents, to);
restore_saved_sigmask_unless(error == -EINTR);
return error;}
SYSCALL_DEFINE6(epoll_pwait, int, epfd, struct epoll_event __user *, events, int, maxevents, int, timeout, const sigset_t __user *, sigmask, size_t, sigsetsize){ struct timespec64 to;
return do_epoll_pwait(epfd, events, maxevents, ep_timeout_to_timespec(&to, timeout), sigmask, sigsetsize);}
SYSCALL_DEFINE6(epoll_pwait2, int, epfd, struct epoll_event __user *, events, int, maxevents, const struct __kernel_timespec __user *, timeout, const sigset_t __user *, sigmask, size_t, sigsetsize){ struct timespec64 ts, *to = NULL;
if (timeout) { if (get_timespec64(&ts, timeout)) return -EFAULT; to = &ts; if (poll_select_set_timeout(to, ts.tv_sec, ts.tv_nsec)) return -EINVAL; }
return do_epoll_pwait(epfd, events, maxevents, to, sigmask, sigsetsize);}
#ifdef CONFIG_KCMPstatic struct epitem *ep_find_tfd(struct eventpoll *ep, int tfd, unsigned long toff){ struct rb_node *rbp; struct epitem *epi;
for (rbp = rb_first_cached(&ep->rbr); rbp; rbp = rb_next(rbp)) { epi = rb_entry(rbp, struct epitem, rbn); if (epi->ffd.fd == tfd) { if (toff == 0) return epi; else toff--; } cond_resched(); }
return NULL;}
struct file *get_epoll_tfile_raw_ptr(struct file *file, int tfd, unsigned long toff){ struct file *file_raw; struct eventpoll *ep; struct epitem *epi;
if (!is_file_epoll(file)) return ERR_PTR(-EINVAL);
ep = file->private_data;
mutex_lock(&ep->mtx); epi = ep_find_tfd(ep, tfd, toff); if (epi) file_raw = epi->ffd.file; else file_raw = ERR_PTR(-ENOENT); mutex_unlock(&ep->mtx);
return file_raw;}#endif /* CONFIG_KCMP */
#ifdef CONFIG_COMPATstatic int do_compat_epoll_pwait(int epfd, struct epoll_event __user *events, int maxevents, struct timespec64 *timeout, const compat_sigset_t __user *sigmask, compat_size_t sigsetsize){ long err;
/* * If the caller wants a certain signal mask to be set during the wait, * we apply it here. */ err = set_compat_user_sigmask(sigmask, sigsetsize); if (err) return err;
err = do_epoll_wait(epfd, events, maxevents, timeout);
restore_saved_sigmask_unless(err == -EINTR);
return err;}
COMPAT_SYSCALL_DEFINE6(epoll_pwait, int, epfd, struct epoll_event __user *, events, int, maxevents, int, timeout, const compat_sigset_t __user *, sigmask, compat_size_t, sigsetsize){ struct timespec64 to;
return do_compat_epoll_pwait(epfd, events, maxevents, ep_timeout_to_timespec(&to, timeout), sigmask, sigsetsize);}
COMPAT_SYSCALL_DEFINE6(epoll_pwait2, int, epfd, struct epoll_event __user *, events, int, maxevents, const struct __kernel_timespec __user *, timeout, const compat_sigset_t __user *, sigmask, compat_size_t, sigsetsize){ struct timespec64 ts, *to = NULL;
if (timeout) { if (get_timespec64(&ts, timeout)) return -EFAULT; to = &ts; if (poll_select_set_timeout(to, ts.tv_sec, ts.tv_nsec)) return -EINVAL; }
return do_compat_epoll_pwait(epfd, events, maxevents, to, sigmask, sigsetsize);}
#endif
static int __init eventpoll_init(void){ struct sysinfo si;
si_meminfo(&si); /* * Allows top 4% of lomem to be allocated for epoll watches (per user). */ max_user_watches = (((si.totalram - si.totalhigh) / 25) << PAGE_SHIFT) / EP_ITEM_COST; BUG_ON(max_user_watches < 0);
/* * We can have many thousands of epitems, so prevent this from * using an extra cache line on 64-bit (and smaller) CPUs */ BUILD_BUG_ON(sizeof(void *) <= 8 && sizeof(struct epitem) > 128);
/* Allocates slab cache used to allocate "struct epitem" items */ epi_cache = kmem_cache_create("eventpoll_epi", sizeof(struct epitem), 0, SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_ACCOUNT, NULL);
/* Allocates slab cache used to allocate "struct eppoll_entry" */ pwq_cache = kmem_cache_create("eventpoll_pwq", sizeof(struct eppoll_entry), 0, SLAB_PANIC|SLAB_ACCOUNT, NULL); epoll_sysctls_init();
ephead_cache = kmem_cache_create("ep_head", sizeof(struct epitems_head), 0, SLAB_PANIC|SLAB_ACCOUNT, NULL);
return 0;}fs_initcall(eventpoll_init);