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/* * include/linux/preempt.h - macros for accessing and manipulating * preempt_count (used for kernel preemption, interrupt count, etc.) */
#include <linux/linkage.h>#include <linux/cleanup.h>#include <linux/types.h>
/* * We put the hardirq and softirq counter into the preemption * counter. The bitmask has the following meaning: * * - bits 0-7 are the preemption count (max preemption depth: 256) * - bits 8-15 are the softirq count (max # of softirqs: 256) * * The hardirq count could in theory be the same as the number of * interrupts in the system, but we run all interrupt handlers with * interrupts disabled, so we cannot have nesting interrupts. Though * there are a few palaeontologic drivers which reenable interrupts in * the handler, so we need more than one bit here. * * PREEMPT_MASK: 0x000000ff * SOFTIRQ_MASK: 0x0000ff00 * HARDIRQ_MASK: 0x000f0000 * NMI_MASK: 0x00f00000 * PREEMPT_NEED_RESCHED: 0x80000000 */#define PREEMPT_BITS 8#define SOFTIRQ_BITS 8#define HARDIRQ_BITS 4#define NMI_BITS 4
#define PREEMPT_SHIFT 0#define SOFTIRQ_SHIFT (PREEMPT_SHIFT + PREEMPT_BITS)#define HARDIRQ_SHIFT (SOFTIRQ_SHIFT + SOFTIRQ_BITS)#define NMI_SHIFT (HARDIRQ_SHIFT + HARDIRQ_BITS)
#define __IRQ_MASK(x) ((1UL << (x))-1)
#define PREEMPT_MASK (__IRQ_MASK(PREEMPT_BITS) << PREEMPT_SHIFT)#define SOFTIRQ_MASK (__IRQ_MASK(SOFTIRQ_BITS) << SOFTIRQ_SHIFT)#define HARDIRQ_MASK (__IRQ_MASK(HARDIRQ_BITS) << HARDIRQ_SHIFT)#define NMI_MASK (__IRQ_MASK(NMI_BITS) << NMI_SHIFT)
#define PREEMPT_OFFSET (1UL << PREEMPT_SHIFT)#define SOFTIRQ_OFFSET (1UL << SOFTIRQ_SHIFT)#define HARDIRQ_OFFSET (1UL << HARDIRQ_SHIFT)#define NMI_OFFSET (1UL << NMI_SHIFT)
#define SOFTIRQ_DISABLE_OFFSET (2 * SOFTIRQ_OFFSET)
#define PREEMPT_DISABLED (PREEMPT_DISABLE_OFFSET + PREEMPT_ENABLED)
/* * Disable preemption until the scheduler is running -- use an unconditional * value so that it also works on !PREEMPT_COUNT kernels. * * Reset by start_kernel()->sched_init()->init_idle()->init_idle_preempt_count(). */#define INIT_PREEMPT_COUNT PREEMPT_OFFSET
/* * Initial preempt_count value; reflects the preempt_count schedule invariant * which states that during context switches: * * preempt_count() == 2*PREEMPT_DISABLE_OFFSET * * Note: PREEMPT_DISABLE_OFFSET is 0 for !PREEMPT_COUNT kernels. * Note: See finish_task_switch(). */#define FORK_PREEMPT_COUNT (2*PREEMPT_DISABLE_OFFSET + PREEMPT_ENABLED)
/* preempt_count() and related functions, depends on PREEMPT_NEED_RESCHED */#include <asm/preempt.h>
/** * interrupt_context_level - return interrupt context level * * Returns the current interrupt context level. * 0 - normal context * 1 - softirq context * 2 - hardirq context * 3 - NMI context */static __always_inline unsigned char interrupt_context_level(void){ unsigned long pc = preempt_count(); unsigned char level = 0;
level += !!(pc & (NMI_MASK)); level += !!(pc & (NMI_MASK | HARDIRQ_MASK)); level += !!(pc & (NMI_MASK | HARDIRQ_MASK | SOFTIRQ_OFFSET));
return level;}
/* * These macro definitions avoid redundant invocations of preempt_count() * because such invocations would result in redundant loads given that * preempt_count() is commonly implemented with READ_ONCE(). */
#define nmi_count() (preempt_count() & NMI_MASK)#define hardirq_count() (preempt_count() & HARDIRQ_MASK)#ifdef CONFIG_PREEMPT_RT# define softirq_count() (current->softirq_disable_cnt & SOFTIRQ_MASK)# define irq_count() ((preempt_count() & (NMI_MASK | HARDIRQ_MASK)) | softirq_count())#else# define softirq_count() (preempt_count() & SOFTIRQ_MASK)# define irq_count() (preempt_count() & (NMI_MASK | HARDIRQ_MASK | SOFTIRQ_MASK))#endif
/* * Macros to retrieve the current execution context: * * in_nmi() - We're in NMI context * in_hardirq() - We're in hard IRQ context * in_serving_softirq() - We're in softirq context * in_task() - We're in task context */#define in_nmi() (nmi_count())#define in_hardirq() (hardirq_count())#define in_serving_softirq() (softirq_count() & SOFTIRQ_OFFSET)#ifdef CONFIG_PREEMPT_RT# define in_task() (!((preempt_count() & (NMI_MASK | HARDIRQ_MASK)) | in_serving_softirq()))#else# define in_task() (!(preempt_count() & (NMI_MASK | HARDIRQ_MASK | SOFTIRQ_OFFSET)))#endif
/* * The following macros are deprecated and should not be used in new code: * in_softirq() - We have BH disabled, or are processing softirqs * in_interrupt() - We're in NMI,IRQ,SoftIRQ context or have BH disabled */#define in_softirq() (softirq_count())#define in_interrupt() (irq_count())
/* * The preempt_count offset after preempt_disable(); */#if defined(CONFIG_PREEMPT_COUNT)# define PREEMPT_DISABLE_OFFSET PREEMPT_OFFSET#else# define PREEMPT_DISABLE_OFFSET 0#endif
/* * The preempt_count offset after spin_lock() */#if !defined(CONFIG_PREEMPT_RT)#define PREEMPT_LOCK_OFFSET PREEMPT_DISABLE_OFFSET#else/* Locks on RT do not disable preemption */#define PREEMPT_LOCK_OFFSET 0#endif
/* * The preempt_count offset needed for things like: * * spin_lock_bh() * * Which need to disable both preemption (CONFIG_PREEMPT_COUNT) and * softirqs, such that unlock sequences of: * * spin_unlock(); * local_bh_enable(); * * Work as expected. */#define SOFTIRQ_LOCK_OFFSET (SOFTIRQ_DISABLE_OFFSET + PREEMPT_LOCK_OFFSET)
/* * Are we running in atomic context? WARNING: this macro cannot * always detect atomic context; in particular, it cannot know about * held spinlocks in non-preemptible kernels. Thus it should not be * used in the general case to determine whether sleeping is possible. * Do not use in_atomic() in driver code. */#define in_atomic() (preempt_count() != 0)
/* * Check whether we were atomic before we did preempt_disable(): * (used by the scheduler) */#define in_atomic_preempt_off() (preempt_count() != PREEMPT_DISABLE_OFFSET)
#if defined(CONFIG_DEBUG_PREEMPT) || defined(CONFIG_TRACE_PREEMPT_TOGGLE)extern void preempt_count_add(int val);extern void preempt_count_sub(int val);#define preempt_count_dec_and_test() \ ({ preempt_count_sub(1); should_resched(0); })#else#define preempt_count_add(val) __preempt_count_add(val)#define preempt_count_sub(val) __preempt_count_sub(val)#define preempt_count_dec_and_test() __preempt_count_dec_and_test()#endif
#define __preempt_count_inc() __preempt_count_add(1)#define __preempt_count_dec() __preempt_count_sub(1)
#define preempt_count_inc() preempt_count_add(1)#define preempt_count_dec() preempt_count_sub(1)
#ifdef CONFIG_PREEMPT_COUNT
#define preempt_disable() \do { \ preempt_count_inc(); \ barrier(); \} while (0)
#define sched_preempt_enable_no_resched() \do { \ barrier(); \ preempt_count_dec(); \} while (0)
#define preempt_enable_no_resched() sched_preempt_enable_no_resched()
#define preemptible() (preempt_count() == 0 && !irqs_disabled())
#ifdef CONFIG_PREEMPTION#define preempt_enable() \do { \ barrier(); \ if (unlikely(preempt_count_dec_and_test())) \ __preempt_schedule(); \} while (0)
#define preempt_enable_notrace() \do { \ barrier(); \ if (unlikely(__preempt_count_dec_and_test())) \ __preempt_schedule_notrace(); \} while (0)
#define preempt_check_resched() \do { \ if (should_resched(0)) \ __preempt_schedule(); \} while (0)
#else /* !CONFIG_PREEMPTION */#define preempt_enable() \do { \ barrier(); \ preempt_count_dec(); \} while (0)
#define preempt_enable_notrace() \do { \ barrier(); \ __preempt_count_dec(); \} while (0)
#define preempt_check_resched() do { } while (0)#endif /* CONFIG_PREEMPTION */
#define preempt_disable_notrace() \do { \ __preempt_count_inc(); \ barrier(); \} while (0)
#define preempt_enable_no_resched_notrace() \do { \ barrier(); \ __preempt_count_dec(); \} while (0)
#else /* !CONFIG_PREEMPT_COUNT */
/* * Even if we don't have any preemption, we need preempt disable/enable * to be barriers, so that we don't have things like get_user/put_user * that can cause faults and scheduling migrate into our preempt-protected * region. */#define preempt_disable() barrier()#define sched_preempt_enable_no_resched() barrier()#define preempt_enable_no_resched() barrier()#define preempt_enable() barrier()#define preempt_check_resched() do { } while (0)
#define preempt_disable_notrace() barrier()#define preempt_enable_no_resched_notrace() barrier()#define preempt_enable_notrace() barrier()#define preemptible() 0
#endif /* CONFIG_PREEMPT_COUNT */
#ifdef MODULE/* * Modules have no business playing preemption tricks. */#undef sched_preempt_enable_no_resched#undef preempt_enable_no_resched#undef preempt_enable_no_resched_notrace#undef preempt_check_resched#endif
#define preempt_set_need_resched() \do { \ set_preempt_need_resched(); \} while (0)#define preempt_fold_need_resched() \do { \ if (tif_need_resched()) \ set_preempt_need_resched(); \} while (0)
#ifdef CONFIG_PREEMPT_NOTIFIERS
struct preempt_notifier;struct task_struct;
/** * preempt_ops - notifiers called when a task is preempted and rescheduled * @sched_in: we're about to be rescheduled: * notifier: struct preempt_notifier for the task being scheduled * cpu: cpu we're scheduled on * @sched_out: we've just been preempted * notifier: struct preempt_notifier for the task being preempted * next: the task that's kicking us out * * Please note that sched_in and out are called under different * contexts. sched_out is called with rq lock held and irq disabled * while sched_in is called without rq lock and irq enabled. This * difference is intentional and depended upon by its users. */struct preempt_ops { void (*sched_in)(struct preempt_notifier *notifier, int cpu); void (*sched_out)(struct preempt_notifier *notifier, struct task_struct *next);};
/** * preempt_notifier - key for installing preemption notifiers * @link: internal use * @ops: defines the notifier functions to be called * * Usually used in conjunction with container_of(). */struct preempt_notifier { struct hlist_node link; struct preempt_ops *ops;};
void preempt_notifier_inc(void);void preempt_notifier_dec(void);void preempt_notifier_register(struct preempt_notifier *notifier);void preempt_notifier_unregister(struct preempt_notifier *notifier);
static inline void preempt_notifier_init(struct preempt_notifier *notifier, struct preempt_ops *ops){ /* INIT_HLIST_NODE() open coded, to avoid dependency on list.h */ notifier->link.next = NULL; notifier->link.pprev = NULL; notifier->ops = ops;}
#endif
/* * Migrate-Disable and why it is undesired. * * When a preempted task becomes eligible to run under the ideal model (IOW it * becomes one of the M highest priority tasks), it might still have to wait * for the preemptee's migrate_disable() section to complete. Thereby suffering * a reduction in bandwidth in the exact duration of the migrate_disable() * section. * * Per this argument, the change from preempt_disable() to migrate_disable() * gets us: * * - a higher priority tasks gains reduced wake-up latency; with preempt_disable() * it would have had to wait for the lower priority task. * * - a lower priority tasks; which under preempt_disable() could've instantly * migrated away when another CPU becomes available, is now constrained * by the ability to push the higher priority task away, which might itself be * in a migrate_disable() section, reducing its available bandwidth. * * IOW it trades latency / moves the interference term, but it stays in the * system, and as long as it remains unbounded, the system is not fully * deterministic. * * * The reason we have it anyway. * * PREEMPT_RT breaks a number of assumptions traditionally held. By forcing a * number of primitives into becoming preemptible, they would also allow * migration. This turns out to break a bunch of per-cpu usage. To this end, * all these primitives employ migrate_disable() to restore this implicit * assumption. * * This is a 'temporary' work-around at best. The correct solution is getting * rid of the above assumptions and reworking the code to employ explicit * per-cpu locking or short preempt-disable regions. * * The end goal must be to get rid of migrate_disable(), alternatively we need * a schedulability theory that does not depend on arbitrary migration. * * * Notes on the implementation. * * The implementation is particularly tricky since existing code patterns * dictate neither migrate_disable() nor migrate_enable() is allowed to block. * This means that it cannot use cpus_read_lock() to serialize against hotplug, * nor can it easily migrate itself into a pending affinity mask change on * migrate_enable(). * * * Note: even non-work-conserving schedulers like semi-partitioned depends on * migration, so migrate_disable() is not only a problem for * work-conserving schedulers. * */
/** * preempt_disable_nested - Disable preemption inside a normally preempt disabled section * * Use for code which requires preemption protection inside a critical * section which has preemption disabled implicitly on non-PREEMPT_RT * enabled kernels, by e.g.: * - holding a spinlock/rwlock * - soft interrupt context * - regular interrupt handlers * * On PREEMPT_RT enabled kernels spinlock/rwlock held sections, soft * interrupt context and regular interrupt handlers are preemptible and * only prevent migration. preempt_disable_nested() ensures that preemption * is disabled for cases which require CPU local serialization even on * PREEMPT_RT. For non-PREEMPT_RT kernels this is a NOP. * * The use cases are code sequences which are not serialized by a * particular lock instance, e.g.: * - seqcount write side critical sections where the seqcount is not * associated to a particular lock and therefore the automatic * protection mechanism does not work. This prevents a live lock * against a preempting high priority reader. * - RMW per CPU variable updates like vmstat. *//* Macro to avoid header recursion hell vs. lockdep */#define preempt_disable_nested() \do { \ if (IS_ENABLED(CONFIG_PREEMPT_RT)) \ preempt_disable(); \ else \ lockdep_assert_preemption_disabled(); \} while (0)
/** * preempt_enable_nested - Undo the effect of preempt_disable_nested() */static __always_inline void preempt_enable_nested(void){ if (IS_ENABLED(CONFIG_PREEMPT_RT)) preempt_enable();}
DEFINE_LOCK_GUARD_0(preempt, preempt_disable(), preempt_enable())DEFINE_LOCK_GUARD_0(preempt_notrace, preempt_disable_notrace(), preempt_enable_notrace())
#ifdef CONFIG_PREEMPT_DYNAMIC
extern bool preempt_model_none(void);extern bool preempt_model_voluntary(void);extern bool preempt_model_full(void);extern bool preempt_model_lazy(void);
#else
static inline bool preempt_model_none(void){ return IS_ENABLED(CONFIG_PREEMPT_NONE);}static inline bool preempt_model_voluntary(void){ return IS_ENABLED(CONFIG_PREEMPT_VOLUNTARY);}static inline bool preempt_model_full(void){ return IS_ENABLED(CONFIG_PREEMPT);}
static inline bool preempt_model_lazy(void){ return IS_ENABLED(CONFIG_PREEMPT_LAZY);}
#endif
static inline bool preempt_model_rt(void){ return IS_ENABLED(CONFIG_PREEMPT_RT);}
extern const char *preempt_model_str(void);
/* * Does the preemption model allow non-cooperative preemption? * * For !CONFIG_PREEMPT_DYNAMIC kernels this is an exact match with * CONFIG_PREEMPTION; for CONFIG_PREEMPT_DYNAMIC this doesn't work as the * kernel is *built* with CONFIG_PREEMPTION=y but may run with e.g. the * PREEMPT_NONE model. */static inline bool preempt_model_preemptible(void){ return preempt_model_full() || preempt_model_lazy() || preempt_model_rt();}
#endif /* __LINUX_PREEMPT_H */