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/* SPDX-License-Identifier: GPL-2.0 */
#ifndef __LINUX_PREEMPT_H
#define __LINUX_PREEMPT_H
/*
* include/linux/preempt.h - macros for accessing and manipulating
* preempt_count (used for kernel preemption, interrupt count, etc.)
*/
#include <linux/linkage.h>
#include <linux/list.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>
#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)
#else
# define softirq_count() (preempt_count() & SOFTIRQ_MASK)
#endif
#define irq_count() (nmi_count() | hardirq_count() | softirq_count())
/*
* 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)
#define in_task() (!(in_nmi() | in_hardirq() | in_serving_softirq()))
/*
* The following macros are deprecated and should not be used in new code:
* in_irq() - Obsolete version of in_hardirq()
* 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_irq() (hardirq_count())
#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()
*/
#define PREEMPT_LOCK_OFFSET PREEMPT_DISABLE_OFFSET
/*
* 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;
/**
* 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(¬ifier->link);
notifier->ops = ops;
}
#endif
#ifdef CONFIG_SMP
/*
* Migrate-Disable and why it is undesired.
*
* When a preempted task becomes elegible 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 it's 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 migirate_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 abritrary 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.
*
*/
extern void migrate_disable(void);
extern void migrate_enable(void);
#else
static inline void migrate_disable(void) { }
static inline void migrate_enable(void) { }
#endif /* CONFIG_SMP */
#endif /* __LINUX_PREEMPT_H */
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