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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/* kernel/rwsem.c: R/W semaphores, public implementation * * Written by David Howells (dhowells@redhat.com). * Derived from asm-i386/semaphore.h * * Writer lock-stealing by Alex Shi <alex.shi@intel.com> * and Michel Lespinasse <walken@google.com> * * Optimistic spinning by Tim Chen <tim.c.chen@intel.com> * and Davidlohr Bueso <davidlohr@hp.com>. Based on mutexes. * * Rwsem count bit fields re-definition and rwsem rearchitecture by * Waiman Long <longman@redhat.com> and * Peter Zijlstra <peterz@infradead.org>. */
#include <linux/types.h>#include <linux/kernel.h>#include <linux/sched.h>#include <linux/sched/rt.h>#include <linux/sched/task.h>#include <linux/sched/debug.h>#include <linux/sched/wake_q.h>#include <linux/sched/signal.h>#include <linux/sched/clock.h>#include <linux/export.h>#include <linux/rwsem.h>#include <linux/atomic.h>#include <linux/hung_task.h>#include <trace/events/lock.h>
#ifndef CONFIG_PREEMPT_RT#include "lock_events.h"
/* * The least significant 2 bits of the owner value has the following * meanings when set. * - Bit 0: RWSEM_READER_OWNED - rwsem may be owned by readers (just a hint) * - Bit 1: RWSEM_NONSPINNABLE - Cannot spin on a reader-owned lock * * When the rwsem is reader-owned and a spinning writer has timed out, * the nonspinnable bit will be set to disable optimistic spinning.
* When a writer acquires a rwsem, it puts its task_struct pointer * into the owner field. It is cleared after an unlock. * * When a reader acquires a rwsem, it will also puts its task_struct * pointer into the owner field with the RWSEM_READER_OWNED bit set. * On unlock, the owner field will largely be left untouched. So * for a free or reader-owned rwsem, the owner value may contain * information about the last reader that acquires the rwsem. * * That information may be helpful in debugging cases where the system * seems to hang on a reader owned rwsem especially if only one reader * is involved. Ideally we would like to track all the readers that own * a rwsem, but the overhead is simply too big. * * A fast path reader optimistic lock stealing is supported when the rwsem * is previously owned by a writer and the following conditions are met: * - rwsem is not currently writer owned * - the handoff isn't set. */#define RWSEM_READER_OWNED (1UL << 0)#define RWSEM_NONSPINNABLE (1UL << 1)#define RWSEM_OWNER_FLAGS_MASK (RWSEM_READER_OWNED | RWSEM_NONSPINNABLE)
#ifdef CONFIG_DEBUG_RWSEMS# define DEBUG_RWSEMS_WARN_ON(c, sem) do { \ if (!debug_locks_silent && \ WARN_ONCE(c, "DEBUG_RWSEMS_WARN_ON(%s): count = 0x%lx, magic = 0x%lx, owner = 0x%lx, curr 0x%lx, list %sempty\n",\ #c, atomic_long_read(&(sem)->count), \ (unsigned long) sem->magic, \ atomic_long_read(&(sem)->owner), (long)current, \ rwsem_is_contended(sem) ? "" : "not ")) \ debug_locks_off(); \ } while (0)#else# define DEBUG_RWSEMS_WARN_ON(c, sem)#endif
/* * On 64-bit architectures, the bit definitions of the count are: * * Bit 0 - writer locked bit * Bit 1 - waiters present bit * Bit 2 - lock handoff bit * Bits 3-7 - reserved * Bits 8-62 - 55-bit reader count * Bit 63 - read fail bit * * On 32-bit architectures, the bit definitions of the count are: * * Bit 0 - writer locked bit * Bit 1 - waiters present bit * Bit 2 - lock handoff bit * Bits 3-7 - reserved * Bits 8-30 - 23-bit reader count * Bit 31 - read fail bit * * It is not likely that the most significant bit (read fail bit) will ever * be set. This guard bit is still checked anyway in the down_read() fastpath * just in case we need to use up more of the reader bits for other purpose * in the future. * * atomic_long_fetch_add() is used to obtain reader lock, whereas * atomic_long_cmpxchg() will be used to obtain writer lock. * * There are three places where the lock handoff bit may be set or cleared. * 1) rwsem_mark_wake() for readers -- set, clear * 2) rwsem_try_write_lock() for writers -- set, clear * 3) rwsem_del_waiter() -- clear * * For all the above cases, wait_lock will be held. A writer must also * be the first one in the wait_list to be eligible for setting the handoff * bit. So concurrent setting/clearing of handoff bit is not possible. */#define RWSEM_WRITER_LOCKED (1UL << 0)#define RWSEM_FLAG_WAITERS (1UL << 1)#define RWSEM_FLAG_HANDOFF (1UL << 2)#define RWSEM_FLAG_READFAIL (1UL << (BITS_PER_LONG - 1))
#define RWSEM_READER_SHIFT 8#define RWSEM_READER_BIAS (1UL << RWSEM_READER_SHIFT)#define RWSEM_READER_MASK (~(RWSEM_READER_BIAS - 1))#define RWSEM_WRITER_MASK RWSEM_WRITER_LOCKED#define RWSEM_LOCK_MASK (RWSEM_WRITER_MASK|RWSEM_READER_MASK)#define RWSEM_READ_FAILED_MASK (RWSEM_WRITER_MASK|RWSEM_FLAG_WAITERS|\ RWSEM_FLAG_HANDOFF|RWSEM_FLAG_READFAIL)
/* * All writes to owner are protected by WRITE_ONCE() to make sure that * store tearing can't happen as optimistic spinners may read and use * the owner value concurrently without lock. Read from owner, however, * may not need READ_ONCE() as long as the pointer value is only used * for comparison and isn't being dereferenced. * * Both rwsem_{set,clear}_owner() functions should be in the same * preempt disable section as the atomic op that changes sem->count. */static inline void rwsem_set_owner(struct rw_semaphore *sem){ lockdep_assert_preemption_disabled(); atomic_long_set(&sem->owner, (long)current);}
static inline void rwsem_clear_owner(struct rw_semaphore *sem){ lockdep_assert_preemption_disabled(); atomic_long_set(&sem->owner, 0);}
/* * Test the flags in the owner field. */static inline bool rwsem_test_oflags(struct rw_semaphore *sem, long flags){ return atomic_long_read(&sem->owner) & flags;}
/* * The task_struct pointer of the last owning reader will be left in * the owner field. * * Note that the owner value just indicates the task has owned the rwsem * previously, it may not be the real owner or one of the real owners * anymore when that field is examined, so take it with a grain of salt. * * The reader non-spinnable bit is preserved. */static inline void __rwsem_set_reader_owned(struct rw_semaphore *sem, struct task_struct *owner){ unsigned long val = (unsigned long)owner | RWSEM_READER_OWNED | (atomic_long_read(&sem->owner) & RWSEM_NONSPINNABLE);
atomic_long_set(&sem->owner, val);}
static inline void rwsem_set_reader_owned(struct rw_semaphore *sem){ __rwsem_set_reader_owned(sem, current);}
#if defined(CONFIG_DEBUG_RWSEMS) || defined(CONFIG_DETECT_HUNG_TASK_BLOCKER)/* * Return just the real task structure pointer of the owner */struct task_struct *rwsem_owner(struct rw_semaphore *sem){ return (struct task_struct *) (atomic_long_read(&sem->owner) & ~RWSEM_OWNER_FLAGS_MASK);}
/* * Return true if the rwsem is owned by a reader. */bool is_rwsem_reader_owned(struct rw_semaphore *sem){ /* * Check the count to see if it is write-locked. */ long count = atomic_long_read(&sem->count);
if (count & RWSEM_WRITER_MASK) return false; return rwsem_test_oflags(sem, RWSEM_READER_OWNED);}
/* * With CONFIG_DEBUG_RWSEMS or CONFIG_DETECT_HUNG_TASK_BLOCKER configured, * it will make sure that the owner field of a reader-owned rwsem either * points to a real reader-owner(s) or gets cleared. The only exception is * when the unlock is done by up_read_non_owner(). */static inline void rwsem_clear_reader_owned(struct rw_semaphore *sem){ unsigned long val = atomic_long_read(&sem->owner);
while ((val & ~RWSEM_OWNER_FLAGS_MASK) == (unsigned long)current) { if (atomic_long_try_cmpxchg(&sem->owner, &val, val & RWSEM_OWNER_FLAGS_MASK)) return; }}#elsestatic inline void rwsem_clear_reader_owned(struct rw_semaphore *sem){}#endif
/* * Set the RWSEM_NONSPINNABLE bits if the RWSEM_READER_OWNED flag * remains set. Otherwise, the operation will be aborted. */static inline void rwsem_set_nonspinnable(struct rw_semaphore *sem){ unsigned long owner = atomic_long_read(&sem->owner);
do { if (!(owner & RWSEM_READER_OWNED)) break; if (owner & RWSEM_NONSPINNABLE) break; } while (!atomic_long_try_cmpxchg(&sem->owner, &owner, owner | RWSEM_NONSPINNABLE));}
static inline bool rwsem_read_trylock(struct rw_semaphore *sem, long *cntp){ *cntp = atomic_long_add_return_acquire(RWSEM_READER_BIAS, &sem->count);
if (WARN_ON_ONCE(*cntp < 0)) rwsem_set_nonspinnable(sem);
if (!(*cntp & RWSEM_READ_FAILED_MASK)) { rwsem_set_reader_owned(sem); return true; }
return false;}
static inline bool rwsem_write_trylock(struct rw_semaphore *sem){ long tmp = RWSEM_UNLOCKED_VALUE;
if (atomic_long_try_cmpxchg_acquire(&sem->count, &tmp, RWSEM_WRITER_LOCKED)) { rwsem_set_owner(sem); return true; }
return false;}
/* * Return the real task structure pointer of the owner and the embedded * flags in the owner. pflags must be non-NULL. */static inline struct task_struct *rwsem_owner_flags(struct rw_semaphore *sem, unsigned long *pflags){ unsigned long owner = atomic_long_read(&sem->owner);
*pflags = owner & RWSEM_OWNER_FLAGS_MASK; return (struct task_struct *)(owner & ~RWSEM_OWNER_FLAGS_MASK);}
/* * Guide to the rw_semaphore's count field. * * When the RWSEM_WRITER_LOCKED bit in count is set, the lock is owned * by a writer. * * The lock is owned by readers when * (1) the RWSEM_WRITER_LOCKED isn't set in count, * (2) some of the reader bits are set in count, and * (3) the owner field has RWSEM_READ_OWNED bit set. * * Having some reader bits set is not enough to guarantee a readers owned * lock as the readers may be in the process of backing out from the count * and a writer has just released the lock. So another writer may steal * the lock immediately after that. */
/* * Initialize an rwsem: */void __init_rwsem(struct rw_semaphore *sem, const char *name, struct lock_class_key *key){#ifdef CONFIG_DEBUG_LOCK_ALLOC /* * Make sure we are not reinitializing a held semaphore: */ debug_check_no_locks_freed((void *)sem, sizeof(*sem)); lockdep_init_map_wait(&sem->dep_map, name, key, 0, LD_WAIT_SLEEP);#endif#ifdef CONFIG_DEBUG_RWSEMS sem->magic = sem;#endif atomic_long_set(&sem->count, RWSEM_UNLOCKED_VALUE); atomic_long_set(&sem->owner, 0L); scoped_guard (raw_spinlock_init, &sem->wait_lock) { sem->first_waiter = NULL; }#ifdef CONFIG_RWSEM_SPIN_ON_OWNER osq_lock_init(&sem->osq);#endif}EXPORT_SYMBOL(__init_rwsem);
enum rwsem_waiter_type { RWSEM_WAITING_FOR_WRITE, RWSEM_WAITING_FOR_READ};
struct rwsem_waiter { struct list_head list; struct task_struct *task; enum rwsem_waiter_type type; unsigned long timeout; bool handoff_set;};
enum rwsem_wake_type { RWSEM_WAKE_ANY, /* Wake whatever's at head of wait list */ RWSEM_WAKE_READERS, /* Wake readers only */ RWSEM_WAKE_READ_OWNED /* Waker thread holds the read lock */};
/* * The typical HZ value is either 250 or 1000. So set the minimum waiting * time to at least 4ms or 1 jiffy (if it is higher than 4ms) in the wait * queue before initiating the handoff protocol. */#define RWSEM_WAIT_TIMEOUT DIV_ROUND_UP(HZ, 250)
/* * Magic number to batch-wakeup waiting readers, even when writers are * also present in the queue. This both limits the amount of work the * waking thread must do and also prevents any potential counter overflow, * however unlikely. */#define MAX_READERS_WAKEUP 0x100
static inlinebool __rwsem_del_waiter(struct rw_semaphore *sem, struct rwsem_waiter *waiter) __must_hold(&sem->wait_lock){ if (list_empty(&waiter->list)) { sem->first_waiter = NULL; return false; }
if (sem->first_waiter == waiter) { sem->first_waiter = list_first_entry(&waiter->list, struct rwsem_waiter, list); } list_del(&waiter->list);
return true;}
/* * Remove a waiter from the wait_list and clear flags. * * Both rwsem_mark_wake() and rwsem_try_write_lock() contain a full 'copy' of * this function. Modify with care. * * Return: true if wait_list isn't empty and false otherwise */static inline boolrwsem_del_waiter(struct rw_semaphore *sem, struct rwsem_waiter *waiter){ lockdep_assert_held(&sem->wait_lock); if (__rwsem_del_waiter(sem, waiter)) return true; atomic_long_andnot(RWSEM_FLAG_HANDOFF | RWSEM_FLAG_WAITERS, &sem->count); return false;}
static inlinestruct rwsem_waiter *next_waiter(const struct rw_semaphore *sem, const struct rwsem_waiter *waiter) __must_hold(&sem->wait_lock){ struct rwsem_waiter *next = list_first_entry(&waiter->list, struct rwsem_waiter, list); if (next == sem->first_waiter) return NULL; return next;}
/* * handle the lock release when processes blocked on it that can now run * - if we come here from up_xxxx(), then the RWSEM_FLAG_WAITERS bit must * have been set. * - there must be someone on the queue * - the wait_lock must be held by the caller * - tasks are marked for wakeup, the caller must later invoke wake_up_q() * to actually wakeup the blocked task(s) and drop the reference count, * preferably when the wait_lock is released * - woken process blocks are discarded from the list after having task zeroed * - writers are only marked woken if downgrading is false * * Implies rwsem_del_waiter() for all woken readers. */static void rwsem_mark_wake(struct rw_semaphore *sem, enum rwsem_wake_type wake_type, struct wake_q_head *wake_q){ struct rwsem_waiter *waiter, *next; long oldcount, woken = 0, adjustment = 0; struct list_head wlist;
lockdep_assert_held(&sem->wait_lock);
/* * Take a peek at the queue head waiter such that we can determine * the wakeup(s) to perform. */ waiter = sem->first_waiter;
if (waiter->type == RWSEM_WAITING_FOR_WRITE) { if (wake_type == RWSEM_WAKE_ANY) { /* * Mark writer at the front of the queue for wakeup. * Until the task is actually later awoken later by * the caller, other writers are able to steal it. * Readers, on the other hand, will block as they * will notice the queued writer. */ wake_q_add(wake_q, waiter->task); lockevent_inc(rwsem_wake_writer); }
return; }
/* * No reader wakeup if there are too many of them already. */ if (unlikely(atomic_long_read(&sem->count) < 0)) return;
/* * Writers might steal the lock before we grant it to the next reader. * We prefer to do the first reader grant before counting readers * so we can bail out early if a writer stole the lock. */ if (wake_type != RWSEM_WAKE_READ_OWNED) { struct task_struct *owner;
adjustment = RWSEM_READER_BIAS; oldcount = atomic_long_fetch_add(adjustment, &sem->count); if (unlikely(oldcount & RWSEM_WRITER_MASK)) { /* * When we've been waiting "too" long (for writers * to give up the lock), request a HANDOFF to * force the issue. */ if (time_after(jiffies, waiter->timeout)) { if (!(oldcount & RWSEM_FLAG_HANDOFF)) { adjustment -= RWSEM_FLAG_HANDOFF; lockevent_inc(rwsem_rlock_handoff); } waiter->handoff_set = true; }
atomic_long_add(-adjustment, &sem->count); return; } /* * Set it to reader-owned to give spinners an early * indication that readers now have the lock. * The reader nonspinnable bit seen at slowpath entry of * the reader is copied over. */ owner = waiter->task; __rwsem_set_reader_owned(sem, owner); }
/* * Grant up to MAX_READERS_WAKEUP read locks to all the readers in the * queue. We know that the woken will be at least 1 as we accounted * for above. Note we increment the 'active part' of the count by the * number of readers before waking any processes up. * * This is an adaptation of the phase-fair R/W locks where at the * reader phase (first waiter is a reader), all readers are eligible * to acquire the lock at the same time irrespective of their order * in the queue. The writers acquire the lock according to their * order in the queue. * * We have to do wakeup in 2 passes to prevent the possibility that * the reader count may be decremented before it is incremented. It * is because the to-be-woken waiter may not have slept yet. So it * may see waiter->task got cleared, finish its critical section and * do an unlock before the reader count increment. * * 1) Collect the read-waiters in a separate list, count them and * fully increment the reader count in rwsem. * 2) For each waiters in the new list, clear waiter->task and * put them into wake_q to be woken up later. */ INIT_LIST_HEAD(&wlist); do { next = next_waiter(sem, waiter); if (waiter->type == RWSEM_WAITING_FOR_WRITE) continue;
woken++; list_move_tail(&waiter->list, &wlist); if (sem->first_waiter == waiter) sem->first_waiter = next;
/* * Limit # of readers that can be woken up per wakeup call. */ if (unlikely(woken >= MAX_READERS_WAKEUP)) break; } while ((waiter = next) != NULL);
adjustment = woken * RWSEM_READER_BIAS - adjustment; lockevent_cond_inc(rwsem_wake_reader, woken);
oldcount = atomic_long_read(&sem->count); if (!sem->first_waiter) { /* * Combined with list_move_tail() above, this implies * rwsem_del_waiter(). */ adjustment -= RWSEM_FLAG_WAITERS; if (oldcount & RWSEM_FLAG_HANDOFF) adjustment -= RWSEM_FLAG_HANDOFF; } else if (woken) { /* * When we've woken a reader, we no longer need to force * writers to give up the lock and we can clear HANDOFF. */ if (oldcount & RWSEM_FLAG_HANDOFF) adjustment -= RWSEM_FLAG_HANDOFF; }
if (adjustment) atomic_long_add(adjustment, &sem->count);
/* 2nd pass */ list_for_each_entry_safe(waiter, next, &wlist, list) { struct task_struct *tsk;
tsk = waiter->task; get_task_struct(tsk);
/* * Ensure calling get_task_struct() before setting the reader * waiter to nil such that rwsem_down_read_slowpath() cannot * race with do_exit() by always holding a reference count * to the task to wakeup. */ smp_store_release(&waiter->task, NULL); /* * Ensure issuing the wakeup (either by us or someone else) * after setting the reader waiter to nil. */ wake_q_add_safe(wake_q, tsk); }}
/* * Remove a waiter and try to wake up other waiters in the wait queue * This function is called from the out_nolock path of both the reader and * writer slowpaths with wait_lock held. It releases the wait_lock and * optionally wake up waiters before it returns. */static inline voidrwsem_del_wake_waiter(struct rw_semaphore *sem, struct rwsem_waiter *waiter, struct wake_q_head *wake_q) __releases(&sem->wait_lock){ bool first = sem->first_waiter == waiter;
wake_q_init(wake_q);
/* * If the wait_list isn't empty and the waiter to be deleted is * the first waiter, we wake up the remaining waiters as they may * be eligible to acquire or spin on the lock. */ if (rwsem_del_waiter(sem, waiter) && first) rwsem_mark_wake(sem, RWSEM_WAKE_ANY, wake_q); raw_spin_unlock_irq(&sem->wait_lock); if (!wake_q_empty(wake_q)) wake_up_q(wake_q);}
/* * This function must be called with the sem->wait_lock held to prevent * race conditions between checking the rwsem wait list and setting the * sem->count accordingly. * * Implies rwsem_del_waiter() on success. */static inline bool rwsem_try_write_lock(struct rw_semaphore *sem, struct rwsem_waiter *waiter) __must_hold(&sem->wait_lock){ struct rwsem_waiter *first = sem->first_waiter; long count, new;
lockdep_assert_held(&sem->wait_lock);
count = atomic_long_read(&sem->count); do { bool has_handoff = !!(count & RWSEM_FLAG_HANDOFF);
if (has_handoff) { /* * Honor handoff bit and yield only when the first * waiter is the one that set it. Otherwisee, we * still try to acquire the rwsem. */ if (first->handoff_set && (waiter != first)) return false; }
new = count;
if (count & RWSEM_LOCK_MASK) { /* * A waiter (first or not) can set the handoff bit * if it is an RT task or wait in the wait queue * for too long. */ if (has_handoff || (!rt_or_dl_task(waiter->task) && !time_after(jiffies, waiter->timeout))) return false;
new |= RWSEM_FLAG_HANDOFF; } else { new |= RWSEM_WRITER_LOCKED; new &= ~RWSEM_FLAG_HANDOFF;
if (list_empty(&first->list)) new &= ~RWSEM_FLAG_WAITERS; } } while (!atomic_long_try_cmpxchg_acquire(&sem->count, &count, new));
/* * We have either acquired the lock with handoff bit cleared or set * the handoff bit. Only the first waiter can have its handoff_set * set here to enable optimistic spinning in slowpath loop. */ if (new & RWSEM_FLAG_HANDOFF) { first->handoff_set = true; lockevent_inc(rwsem_wlock_handoff); return false; }
/* * Have rwsem_try_write_lock() fully imply rwsem_del_waiter() on * success. */ __rwsem_del_waiter(sem, waiter);
rwsem_set_owner(sem); return true;}
/* * The rwsem_spin_on_owner() function returns the following 4 values * depending on the lock owner state. * OWNER_NULL : owner is currently NULL * OWNER_WRITER: when owner changes and is a writer * OWNER_READER: when owner changes and the new owner may be a reader. * OWNER_NONSPINNABLE: * when optimistic spinning has to stop because either the * owner stops running, is unknown, or its timeslice has * been used up. */enum owner_state { OWNER_NULL = 1 << 0, OWNER_WRITER = 1 << 1, OWNER_READER = 1 << 2, OWNER_NONSPINNABLE = 1 << 3,};
#ifdef CONFIG_RWSEM_SPIN_ON_OWNER/* * Try to acquire write lock before the writer has been put on wait queue. */static inline bool rwsem_try_write_lock_unqueued(struct rw_semaphore *sem){ long count = atomic_long_read(&sem->count);
while (!(count & (RWSEM_LOCK_MASK|RWSEM_FLAG_HANDOFF))) { if (atomic_long_try_cmpxchg_acquire(&sem->count, &count, count | RWSEM_WRITER_LOCKED)) { rwsem_set_owner(sem); lockevent_inc(rwsem_opt_lock); return true; } } return false;}
static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem){ struct task_struct *owner; unsigned long flags; bool ret = true;
if (need_resched()) { lockevent_inc(rwsem_opt_fail); return false; }
/* * Disable preemption is equal to the RCU read-side crital section, * thus the task_strcut structure won't go away. */ owner = rwsem_owner_flags(sem, &flags); /* * Don't check the read-owner as the entry may be stale. */ if ((flags & RWSEM_NONSPINNABLE) || (owner && !(flags & RWSEM_READER_OWNED) && !owner_on_cpu(owner))) ret = false;
lockevent_cond_inc(rwsem_opt_fail, !ret); return ret;}
static inline enum owner_staterwsem_owner_state(struct task_struct *owner, unsigned long flags){ if (flags & RWSEM_NONSPINNABLE) return OWNER_NONSPINNABLE;
if (flags & RWSEM_READER_OWNED) return OWNER_READER;
return owner ? OWNER_WRITER : OWNER_NULL;}
static noinline enum owner_staterwsem_spin_on_owner(struct rw_semaphore *sem){ struct task_struct *new, *owner; unsigned long flags, new_flags; enum owner_state state;
lockdep_assert_preemption_disabled();
owner = rwsem_owner_flags(sem, &flags); state = rwsem_owner_state(owner, flags); if (state != OWNER_WRITER) return state;
for (;;) { /* * When a waiting writer set the handoff flag, it may spin * on the owner as well. Once that writer acquires the lock, * we can spin on it. So we don't need to quit even when the * handoff bit is set. */ new = rwsem_owner_flags(sem, &new_flags); if ((new != owner) || (new_flags != flags)) { state = rwsem_owner_state(new, new_flags); break; }
/* * Ensure we emit the owner->on_cpu, dereference _after_ * checking sem->owner still matches owner, if that fails, * owner might point to free()d memory, if it still matches, * our spinning context already disabled preemption which is * equal to RCU read-side crital section ensures the memory * stays valid. */ barrier();
if (need_resched() || !owner_on_cpu(owner)) { state = OWNER_NONSPINNABLE; break; }
cpu_relax(); }
return state;}
/* * Calculate reader-owned rwsem spinning threshold for writer * * The more readers own the rwsem, the longer it will take for them to * wind down and free the rwsem. So the empirical formula used to * determine the actual spinning time limit here is: * * Spinning threshold = (10 + nr_readers/2)us * * The limit is capped to a maximum of 25us (30 readers). This is just * a heuristic and is subjected to change in the future. */static inline u64 rwsem_rspin_threshold(struct rw_semaphore *sem){ long count = atomic_long_read(&sem->count); int readers = count >> RWSEM_READER_SHIFT; u64 delta;
if (readers > 30) readers = 30; delta = (20 + readers) * NSEC_PER_USEC / 2;
return sched_clock() + delta;}
static bool rwsem_optimistic_spin(struct rw_semaphore *sem){ bool taken = false; int prev_owner_state = OWNER_NULL; int loop = 0; u64 rspin_threshold = 0;
/* sem->wait_lock should not be held when doing optimistic spinning */ if (!osq_lock(&sem->osq)) goto done;
/* * Optimistically spin on the owner field and attempt to acquire the * lock whenever the owner changes. Spinning will be stopped when: * 1) the owning writer isn't running; or * 2) readers own the lock and spinning time has exceeded limit. */ for (;;) { enum owner_state owner_state;
owner_state = rwsem_spin_on_owner(sem); if (owner_state == OWNER_NONSPINNABLE) break;
/* * Try to acquire the lock */ taken = rwsem_try_write_lock_unqueued(sem);
if (taken) break;
/* * Time-based reader-owned rwsem optimistic spinning */ if (owner_state == OWNER_READER) { /* * Re-initialize rspin_threshold every time when * the owner state changes from non-reader to reader. * This allows a writer to steal the lock in between * 2 reader phases and have the threshold reset at * the beginning of the 2nd reader phase. */ if (prev_owner_state != OWNER_READER) { if (rwsem_test_oflags(sem, RWSEM_NONSPINNABLE)) break; rspin_threshold = rwsem_rspin_threshold(sem); loop = 0; }
/* * Check time threshold once every 16 iterations to * avoid calling sched_clock() too frequently so * as to reduce the average latency between the times * when the lock becomes free and when the spinner * is ready to do a trylock. */ else if (!(++loop & 0xf) && (sched_clock() > rspin_threshold)) { rwsem_set_nonspinnable(sem); lockevent_inc(rwsem_opt_nospin); break; } }
/* * An RT task cannot do optimistic spinning if it cannot * be sure the lock holder is running or live-lock may * happen if the current task and the lock holder happen * to run in the same CPU. However, aborting optimistic * spinning while a NULL owner is detected may miss some * opportunity where spinning can continue without causing * problem. * * There are 2 possible cases where an RT task may be able * to continue spinning. * * 1) The lock owner is in the process of releasing the * lock, sem->owner is cleared but the lock has not * been released yet. * 2) The lock was free and owner cleared, but another * task just comes in and acquire the lock before * we try to get it. The new owner may be a spinnable * writer. * * To take advantage of two scenarios listed above, the RT * task is made to retry one more time to see if it can * acquire the lock or continue spinning on the new owning * writer. Of course, if the time lag is long enough or the * new owner is not a writer or spinnable, the RT task will * quit spinning. * * If the owner is a writer, the need_resched() check is * done inside rwsem_spin_on_owner(). If the owner is not * a writer, need_resched() check needs to be done here. */ if (owner_state != OWNER_WRITER) { if (need_resched()) break; if (rt_or_dl_task(current) && (prev_owner_state != OWNER_WRITER)) break; } prev_owner_state = owner_state;
/* * The cpu_relax() call is a compiler barrier which forces * everything in this loop to be re-loaded. We don't need * memory barriers as we'll eventually observe the right * values at the cost of a few extra spins. */ cpu_relax(); } osq_unlock(&sem->osq);done: lockevent_cond_inc(rwsem_opt_fail, !taken); return taken;}
/* * Clear the owner's RWSEM_NONSPINNABLE bit if it is set. This should * only be called when the reader count reaches 0. */static inline void clear_nonspinnable(struct rw_semaphore *sem){ if (unlikely(rwsem_test_oflags(sem, RWSEM_NONSPINNABLE))) atomic_long_andnot(RWSEM_NONSPINNABLE, &sem->owner);}
#elsestatic inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem){ return false;}
static inline bool rwsem_optimistic_spin(struct rw_semaphore *sem){ return false;}
static inline void clear_nonspinnable(struct rw_semaphore *sem) { }
static inline enum owner_staterwsem_spin_on_owner(struct rw_semaphore *sem){ return OWNER_NONSPINNABLE;}#endif
/* * Prepare to wake up waiter(s) in the wait queue by putting them into the * given wake_q if the rwsem lock owner isn't a writer. If rwsem is likely * reader-owned, wake up read lock waiters in queue front or wake up any * front waiter otherwise.
* This is being called from both reader and writer slow paths. */static inline void rwsem_cond_wake_waiter(struct rw_semaphore *sem, long count, struct wake_q_head *wake_q){ enum rwsem_wake_type wake_type;
if (count & RWSEM_WRITER_MASK) return;
if (count & RWSEM_READER_MASK) { wake_type = RWSEM_WAKE_READERS; } else { wake_type = RWSEM_WAKE_ANY; clear_nonspinnable(sem); } rwsem_mark_wake(sem, wake_type, wake_q);}
/* * Wait for the read lock to be granted */static struct rw_semaphore __sched *rwsem_down_read_slowpath(struct rw_semaphore *sem, long count, unsigned int state){ long adjustment = -RWSEM_READER_BIAS; long rcnt = (count >> RWSEM_READER_SHIFT); struct rwsem_waiter waiter, *first; DEFINE_WAKE_Q(wake_q);
/* * To prevent a constant stream of readers from starving a sleeping * writer, don't attempt optimistic lock stealing if the lock is * very likely owned by readers. */ if ((atomic_long_read(&sem->owner) & RWSEM_READER_OWNED) && (rcnt > 1) && !(count & RWSEM_WRITER_LOCKED)) goto queue;
/* * Reader optimistic lock stealing. */ if (!(count & (RWSEM_WRITER_LOCKED | RWSEM_FLAG_HANDOFF))) { rwsem_set_reader_owned(sem); lockevent_inc(rwsem_rlock_steal);
/* * Wake up other readers in the wait queue if it is * the first reader. */ if ((rcnt == 1) && (count & RWSEM_FLAG_WAITERS)) { raw_spin_lock_irq(&sem->wait_lock); if (sem->first_waiter) rwsem_mark_wake(sem, RWSEM_WAKE_READ_OWNED, &wake_q); raw_spin_unlock_irq(&sem->wait_lock); wake_up_q(&wake_q); } return sem; }
queue: waiter.task = current; waiter.type = RWSEM_WAITING_FOR_READ; waiter.timeout = jiffies + RWSEM_WAIT_TIMEOUT; waiter.handoff_set = false;
raw_spin_lock_irq(&sem->wait_lock); first = sem->first_waiter; if (!first) { /* * In case the wait queue is empty and the lock isn't owned * by a writer, this reader can exit the slowpath and return * immediately as its RWSEM_READER_BIAS has already been set * in the count. */ if (!(atomic_long_read(&sem->count) & RWSEM_WRITER_MASK)) { /* Provide lock ACQUIRE */ smp_acquire__after_ctrl_dep(); raw_spin_unlock_irq(&sem->wait_lock); rwsem_set_reader_owned(sem); lockevent_inc(rwsem_rlock_fast); return sem; } adjustment += RWSEM_FLAG_WAITERS; INIT_LIST_HEAD(&waiter.list); sem->first_waiter = &waiter; } else { list_add_tail(&waiter.list, &first->list); }
/* we're now waiting on the lock, but no longer actively locking */ count = atomic_long_add_return(adjustment, &sem->count);
rwsem_cond_wake_waiter(sem, count, &wake_q); raw_spin_unlock_irq(&sem->wait_lock);
if (!wake_q_empty(&wake_q)) wake_up_q(&wake_q);
trace_contention_begin(sem, LCB_F_READ); set_current_state(state);
if (state == TASK_UNINTERRUPTIBLE) hung_task_set_blocker(sem, BLOCKER_TYPE_RWSEM_READER);
/* wait to be given the lock */ for (;;) { if (!smp_load_acquire(&waiter.task)) { /* Matches rwsem_mark_wake()'s smp_store_release(). */ break; } if (signal_pending_state(state, current)) { raw_spin_lock_irq(&sem->wait_lock); if (waiter.task) goto out_nolock; raw_spin_unlock_irq(&sem->wait_lock); /* Ordered by sem->wait_lock against rwsem_mark_wake(). */ break; } schedule_preempt_disabled(); lockevent_inc(rwsem_sleep_reader); set_current_state(state); }
if (state == TASK_UNINTERRUPTIBLE) hung_task_clear_blocker();
__set_current_state(TASK_RUNNING); lockevent_inc(rwsem_rlock); trace_contention_end(sem, 0); return sem;
out_nolock: rwsem_del_wake_waiter(sem, &waiter, &wake_q); __set_current_state(TASK_RUNNING); lockevent_inc(rwsem_rlock_fail); trace_contention_end(sem, -EINTR); return ERR_PTR(-EINTR);}
/* * Wait until we successfully acquire the write lock */static struct rw_semaphore __sched *rwsem_down_write_slowpath(struct rw_semaphore *sem, int state){ struct rwsem_waiter waiter, *first; DEFINE_WAKE_Q(wake_q);
/* do optimistic spinning and steal lock if possible */ if (rwsem_can_spin_on_owner(sem) && rwsem_optimistic_spin(sem)) { /* rwsem_optimistic_spin() implies ACQUIRE on success */ return sem; }
/* * Optimistic spinning failed, proceed to the slowpath * and block until we can acquire the sem. */ waiter.task = current; waiter.type = RWSEM_WAITING_FOR_WRITE; waiter.timeout = jiffies + RWSEM_WAIT_TIMEOUT; waiter.handoff_set = false;
raw_spin_lock_irq(&sem->wait_lock);
first = sem->first_waiter; if (first) { list_add_tail(&waiter.list, &first->list); rwsem_cond_wake_waiter(sem, atomic_long_read(&sem->count), &wake_q); if (!wake_q_empty(&wake_q)) { /* * We want to minimize wait_lock hold time especially * when a large number of readers are to be woken up. */ raw_spin_unlock_irq(&sem->wait_lock); wake_up_q(&wake_q); raw_spin_lock_irq(&sem->wait_lock); } } else { INIT_LIST_HEAD(&waiter.list); sem->first_waiter = &waiter; atomic_long_or(RWSEM_FLAG_WAITERS, &sem->count); }
/* wait until we successfully acquire the lock */ set_current_state(state); trace_contention_begin(sem, LCB_F_WRITE);
if (state == TASK_UNINTERRUPTIBLE) hung_task_set_blocker(sem, BLOCKER_TYPE_RWSEM_WRITER);
for (;;) { if (rwsem_try_write_lock(sem, &waiter)) { /* rwsem_try_write_lock() implies ACQUIRE on success */ break; }
raw_spin_unlock_irq(&sem->wait_lock);
if (signal_pending_state(state, current)) goto out_nolock;
/* * After setting the handoff bit and failing to acquire * the lock, attempt to spin on owner to accelerate lock * transfer. If the previous owner is a on-cpu writer and it * has just released the lock, OWNER_NULL will be returned. * In this case, we attempt to acquire the lock again * without sleeping. */ if (waiter.handoff_set) { enum owner_state owner_state;
owner_state = rwsem_spin_on_owner(sem); if (owner_state == OWNER_NULL) goto trylock_again; }
schedule_preempt_disabled(); lockevent_inc(rwsem_sleep_writer); set_current_state(state);trylock_again: raw_spin_lock_irq(&sem->wait_lock); }
if (state == TASK_UNINTERRUPTIBLE) hung_task_clear_blocker();
__set_current_state(TASK_RUNNING); raw_spin_unlock_irq(&sem->wait_lock); lockevent_inc(rwsem_wlock); trace_contention_end(sem, 0); return sem;
out_nolock: __set_current_state(TASK_RUNNING); raw_spin_lock_irq(&sem->wait_lock); rwsem_del_wake_waiter(sem, &waiter, &wake_q); lockevent_inc(rwsem_wlock_fail); trace_contention_end(sem, -EINTR); return ERR_PTR(-EINTR);}
/* * handle waking up a waiter on the semaphore * - up_read/up_write has decremented the active part of count if we come here */static struct rw_semaphore *rwsem_wake(struct rw_semaphore *sem){ unsigned long flags; DEFINE_WAKE_Q(wake_q);
raw_spin_lock_irqsave(&sem->wait_lock, flags);
if (sem->first_waiter) rwsem_mark_wake(sem, RWSEM_WAKE_ANY, &wake_q);
raw_spin_unlock_irqrestore(&sem->wait_lock, flags); wake_up_q(&wake_q);
return sem;}
/* * downgrade a write lock into a read lock * - caller incremented waiting part of count and discovered it still negative * - just wake up any readers at the front of the queue */static struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem){ unsigned long flags; DEFINE_WAKE_Q(wake_q);
raw_spin_lock_irqsave(&sem->wait_lock, flags);
if (sem->first_waiter) rwsem_mark_wake(sem, RWSEM_WAKE_READ_OWNED, &wake_q);
raw_spin_unlock_irqrestore(&sem->wait_lock, flags); wake_up_q(&wake_q);
return sem;}
/* * lock for reading */static __always_inline int __down_read_common(struct rw_semaphore *sem, int state){ int ret = 0; long count;
preempt_disable(); if (!rwsem_read_trylock(sem, &count)) { if (IS_ERR(rwsem_down_read_slowpath(sem, count, state))) { ret = -EINTR; goto out; } DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem); }out: preempt_enable(); return ret;}
static __always_inline void __down_read(struct rw_semaphore *sem){ __down_read_common(sem, TASK_UNINTERRUPTIBLE);}
static __always_inline int __down_read_interruptible(struct rw_semaphore *sem){ return __down_read_common(sem, TASK_INTERRUPTIBLE);}
static __always_inline int __down_read_killable(struct rw_semaphore *sem){ return __down_read_common(sem, TASK_KILLABLE);}
static inline int __down_read_trylock(struct rw_semaphore *sem){ int ret = 0; long tmp;
DEBUG_RWSEMS_WARN_ON(sem->magic != sem, sem);
preempt_disable(); tmp = atomic_long_read(&sem->count); while (!(tmp & RWSEM_READ_FAILED_MASK)) { if (atomic_long_try_cmpxchg_acquire(&sem->count, &tmp, tmp + RWSEM_READER_BIAS)) { rwsem_set_reader_owned(sem); ret = 1; break; } } preempt_enable(); return ret;}
/* * lock for writing */static __always_inline int __down_write_common(struct rw_semaphore *sem, int state){ int ret = 0;
preempt_disable(); if (unlikely(!rwsem_write_trylock(sem))) { if (IS_ERR(rwsem_down_write_slowpath(sem, state))) ret = -EINTR; } preempt_enable(); return ret;}
static __always_inline void __down_write(struct rw_semaphore *sem){ __down_write_common(sem, TASK_UNINTERRUPTIBLE);}
static __always_inline int __down_write_killable(struct rw_semaphore *sem){ return __down_write_common(sem, TASK_KILLABLE);}
static inline int __down_write_trylock(struct rw_semaphore *sem){ int ret;
preempt_disable(); DEBUG_RWSEMS_WARN_ON(sem->magic != sem, sem); ret = rwsem_write_trylock(sem); preempt_enable();
return ret;}
/* * unlock after reading */static inline void __up_read(struct rw_semaphore *sem){ long tmp;
DEBUG_RWSEMS_WARN_ON(sem->magic != sem, sem); DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);
preempt_disable(); rwsem_clear_reader_owned(sem); tmp = atomic_long_add_return_release(-RWSEM_READER_BIAS, &sem->count); DEBUG_RWSEMS_WARN_ON(tmp < 0, sem); if (trace_contended_release_enabled() && (tmp & RWSEM_FLAG_WAITERS)) trace_call__contended_release(sem); if (unlikely((tmp & (RWSEM_LOCK_MASK|RWSEM_FLAG_WAITERS)) == RWSEM_FLAG_WAITERS)) { clear_nonspinnable(sem); rwsem_wake(sem); } preempt_enable();}
/* * unlock after writing */static inline void __up_write(struct rw_semaphore *sem){ long tmp;
DEBUG_RWSEMS_WARN_ON(sem->magic != sem, sem); /* * sem->owner may differ from current if the ownership is transferred * to an anonymous writer by setting the RWSEM_NONSPINNABLE bits. */ DEBUG_RWSEMS_WARN_ON((rwsem_owner(sem) != current) && !rwsem_test_oflags(sem, RWSEM_NONSPINNABLE), sem);
preempt_disable(); rwsem_clear_owner(sem); tmp = atomic_long_fetch_add_release(-RWSEM_WRITER_LOCKED, &sem->count); if (unlikely(tmp & RWSEM_FLAG_WAITERS)) { trace_contended_release(sem); rwsem_wake(sem); } preempt_enable();}
/* * downgrade write lock to read lock */static inline void __downgrade_write(struct rw_semaphore *sem){ long tmp;
/* * When downgrading from exclusive to shared ownership, * anything inside the write-locked region cannot leak * into the read side. In contrast, anything in the * read-locked region is ok to be re-ordered into the * write side. As such, rely on RELEASE semantics. */ DEBUG_RWSEMS_WARN_ON(rwsem_owner(sem) != current, sem); preempt_disable(); tmp = atomic_long_fetch_add_release( -RWSEM_WRITER_LOCKED+RWSEM_READER_BIAS, &sem->count); rwsem_set_reader_owned(sem); if (tmp & RWSEM_FLAG_WAITERS) { trace_contended_release(sem); rwsem_downgrade_wake(sem); } preempt_enable();}
#else /* !CONFIG_PREEMPT_RT */
#define RT_MUTEX_BUILD_MUTEX#include "rtmutex.c"
#define rwbase_set_and_save_current_state(state) \ set_current_state(state)
#define rwbase_restore_current_state() \ __set_current_state(TASK_RUNNING)
#define rwbase_rtmutex_lock_state(rtm, state) \ __rt_mutex_lock(rtm, state)
#define rwbase_rtmutex_slowlock_locked(rtm, state, wq) \ __rt_mutex_slowlock_locked(rtm, NULL, state, wq)
#define rwbase_rtmutex_unlock(rtm) \ __rt_mutex_unlock(rtm)
#define rwbase_rtmutex_trylock(rtm) \ __rt_mutex_trylock(rtm)
#define rwbase_signal_pending_state(state, current) \ signal_pending_state(state, current)
#define rwbase_pre_schedule() \ rt_mutex_pre_schedule()
#define rwbase_schedule() \ rt_mutex_schedule()
#define rwbase_post_schedule() \ rt_mutex_post_schedule()
#include "rwbase_rt.c"
void __init_rwsem(struct rw_semaphore *sem, const char *name, struct lock_class_key *key){ init_rwbase_rt(&(sem)->rwbase);
#ifdef CONFIG_DEBUG_LOCK_ALLOC debug_check_no_locks_freed((void *)sem, sizeof(*sem)); lockdep_init_map_wait(&sem->dep_map, name, key, 0, LD_WAIT_SLEEP);#endif}EXPORT_SYMBOL(__init_rwsem);
static inline void __down_read(struct rw_semaphore *sem){ rwbase_read_lock(&sem->rwbase, TASK_UNINTERRUPTIBLE);}
static inline int __down_read_interruptible(struct rw_semaphore *sem){ return rwbase_read_lock(&sem->rwbase, TASK_INTERRUPTIBLE);}
static inline int __down_read_killable(struct rw_semaphore *sem){ return rwbase_read_lock(&sem->rwbase, TASK_KILLABLE);}
static inline int __down_read_trylock(struct rw_semaphore *sem){ return rwbase_read_trylock(&sem->rwbase);}
static inline void __up_read(struct rw_semaphore *sem){ rwbase_read_unlock(&sem->rwbase, TASK_NORMAL);}
static inline void __sched __down_write(struct rw_semaphore *sem){ rwbase_write_lock(&sem->rwbase, TASK_UNINTERRUPTIBLE);}
static inline int __sched __down_write_killable(struct rw_semaphore *sem){ return rwbase_write_lock(&sem->rwbase, TASK_KILLABLE);}
static inline int __down_write_trylock(struct rw_semaphore *sem){ return rwbase_write_trylock(&sem->rwbase);}
static inline void __up_write(struct rw_semaphore *sem){ rwbase_write_unlock(&sem->rwbase);}
static inline void __downgrade_write(struct rw_semaphore *sem){ rwbase_write_downgrade(&sem->rwbase);}
/* Debug stubs for the common API */#define DEBUG_RWSEMS_WARN_ON(c, sem)
static inline void __rwsem_set_reader_owned(struct rw_semaphore *sem, struct task_struct *owner){}
static inline bool is_rwsem_reader_owned(struct rw_semaphore *sem){ int count = atomic_read(&sem->rwbase.readers);
return count < 0 && count != READER_BIAS;}
#endif /* CONFIG_PREEMPT_RT */
/* * lock for reading */void __sched down_read(struct rw_semaphore *sem) __no_context_analysis{ might_sleep(); rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_);
LOCK_CONTENDED(sem, __down_read_trylock, __down_read);}EXPORT_SYMBOL(down_read);
int __sched down_read_interruptible(struct rw_semaphore *sem) __no_context_analysis{ might_sleep(); rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_);
if (LOCK_CONTENDED_RETURN(sem, __down_read_trylock, __down_read_interruptible)) { rwsem_release(&sem->dep_map, _RET_IP_); return -EINTR; }
return 0;}EXPORT_SYMBOL(down_read_interruptible);
int __sched down_read_killable(struct rw_semaphore *sem) __no_context_analysis{ might_sleep(); rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_);
if (LOCK_CONTENDED_RETURN(sem, __down_read_trylock, __down_read_killable)) { rwsem_release(&sem->dep_map, _RET_IP_); return -EINTR; }
return 0;}EXPORT_SYMBOL(down_read_killable);
/* * trylock for reading -- returns 1 if successful, 0 if contention */int down_read_trylock(struct rw_semaphore *sem) __no_context_analysis{ int ret = __down_read_trylock(sem);
if (ret == 1) rwsem_acquire_read(&sem->dep_map, 0, 1, _RET_IP_); return ret;}EXPORT_SYMBOL(down_read_trylock);
/* * lock for writing */void __sched down_write(struct rw_semaphore *sem) __no_context_analysis{ might_sleep(); rwsem_acquire(&sem->dep_map, 0, 0, _RET_IP_); LOCK_CONTENDED(sem, __down_write_trylock, __down_write);}EXPORT_SYMBOL(down_write);
/* * lock for writing */int __sched down_write_killable(struct rw_semaphore *sem) __no_context_analysis{ might_sleep(); rwsem_acquire(&sem->dep_map, 0, 0, _RET_IP_);
if (LOCK_CONTENDED_RETURN(sem, __down_write_trylock, __down_write_killable)) { rwsem_release(&sem->dep_map, _RET_IP_); return -EINTR; }
return 0;}EXPORT_SYMBOL(down_write_killable);
/* * trylock for writing -- returns 1 if successful, 0 if contention */int down_write_trylock(struct rw_semaphore *sem) __no_context_analysis{ int ret = __down_write_trylock(sem);
if (ret == 1) rwsem_acquire(&sem->dep_map, 0, 1, _RET_IP_);
return ret;}EXPORT_SYMBOL(down_write_trylock);
/* * release a read lock */void up_read(struct rw_semaphore *sem) __no_context_analysis{ rwsem_release(&sem->dep_map, _RET_IP_); __up_read(sem);}EXPORT_SYMBOL(up_read);
/* * release a write lock */void up_write(struct rw_semaphore *sem) __no_context_analysis{ rwsem_release(&sem->dep_map, _RET_IP_); __up_write(sem);}EXPORT_SYMBOL(up_write);
/* * downgrade write lock to read lock */void downgrade_write(struct rw_semaphore *sem) __no_context_analysis{ lock_downgrade(&sem->dep_map, _RET_IP_); __downgrade_write(sem);}EXPORT_SYMBOL(downgrade_write);
#ifdef CONFIG_DEBUG_LOCK_ALLOC
void down_read_nested(struct rw_semaphore *sem, int subclass) __no_context_analysis{ might_sleep(); rwsem_acquire_read(&sem->dep_map, subclass, 0, _RET_IP_); LOCK_CONTENDED(sem, __down_read_trylock, __down_read);}EXPORT_SYMBOL(down_read_nested);
int down_read_killable_nested(struct rw_semaphore *sem, int subclass) __no_context_analysis{ might_sleep(); rwsem_acquire_read(&sem->dep_map, subclass, 0, _RET_IP_);
if (LOCK_CONTENDED_RETURN(sem, __down_read_trylock, __down_read_killable)) { rwsem_release(&sem->dep_map, _RET_IP_); return -EINTR; }
return 0;}EXPORT_SYMBOL(down_read_killable_nested);
void _down_write_nest_lock(struct rw_semaphore *sem, struct lockdep_map *nest) __no_context_analysis{ might_sleep(); rwsem_acquire_nest(&sem->dep_map, 0, 0, nest, _RET_IP_); LOCK_CONTENDED(sem, __down_write_trylock, __down_write);}EXPORT_SYMBOL(_down_write_nest_lock);
void down_read_non_owner(struct rw_semaphore *sem) __no_context_analysis{ might_sleep(); __down_read(sem); /* * The owner value for a reader-owned lock is mostly for debugging * purpose only and is not critical to the correct functioning of * rwsem. So it is perfectly fine to set it in a preempt-enabled * context here. */ __rwsem_set_reader_owned(sem, NULL);}EXPORT_SYMBOL(down_read_non_owner);
void down_write_nested(struct rw_semaphore *sem, int subclass) __no_context_analysis{ might_sleep(); rwsem_acquire(&sem->dep_map, subclass, 0, _RET_IP_); LOCK_CONTENDED(sem, __down_write_trylock, __down_write);}EXPORT_SYMBOL(down_write_nested);
int __sched down_write_killable_nested(struct rw_semaphore *sem, int subclass) __no_context_analysis{ might_sleep(); rwsem_acquire(&sem->dep_map, subclass, 0, _RET_IP_);
if (LOCK_CONTENDED_RETURN(sem, __down_write_trylock, __down_write_killable)) { rwsem_release(&sem->dep_map, _RET_IP_); return -EINTR; }
return 0;}EXPORT_SYMBOL(down_write_killable_nested);
void up_read_non_owner(struct rw_semaphore *sem) __no_context_analysis{ DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem); __up_read(sem);}EXPORT_SYMBOL(up_read_non_owner);
#endif