include/linux/preempt.h - kernel/common - Git at Google

 #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:	0x00100000
  * PREEMPT_NEED_RESCHED:	0x80000000
  */
 #define PREEMPT_BITS	8
 #define SOFTIRQ_BITS	8
 #define HARDIRQ_BITS	4
 #define NMI_BITS	1

 #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)

 /* We use the MSB mostly because its available */
 #define PREEMPT_NEED_RESCHED	0x80000000

 /* preempt_count() and related functions, depends on PREEMPT_NEED_RESCHED */
 #include <asm/preempt.h>

 #define hardirq_count()	(preempt_count() & HARDIRQ_MASK)
 #define softirq_count()	(preempt_count() & SOFTIRQ_MASK)
 #define irq_count()	(preempt_count() & (HARDIRQ_MASK | SOFTIRQ_MASK \
 				 | NMI_MASK))

 /*
  * Are we doing bottom half or hardware interrupt processing?
  * Are we in a softirq context? Interrupt context?
  * in_softirq - Are we currently processing softirq or have bh disabled?
  * in_serving_softirq - Are we currently processing softirq?
  */
 #define in_irq()		(hardirq_count())
 #define in_softirq()		(softirq_count())
 #define in_interrupt()		(irq_count())
 #define in_serving_softirq()	(softirq_count() & SOFTIRQ_OFFSET)

 /*
  * Are we in NMI context?
  */
 #define in_nmi()	(preempt_count() & NMI_MASK)

 /*
  * 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_PREEMPT_TRACER)
 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_PREEMPT
 #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_PREEMPT */
 #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_PREEMPT */

 #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(&notifier->link);
 	notifier->ops = ops;
 }

 #endif

 #endif /* __LINUX_PREEMPT_H */
	#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: 0x00100000
	* PREEMPT_NEED_RESCHED: 0x80000000
	*/
	#define PREEMPT_BITS 8
	#define SOFTIRQ_BITS 8
	#define HARDIRQ_BITS 4
	#define NMI_BITS 1

	#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)

	/* We use the MSB mostly because its available */
	#define PREEMPT_NEED_RESCHED 0x80000000

	/* preempt_count() and related functions, depends on PREEMPT_NEED_RESCHED */
	#include <asm/preempt.h>

	#define hardirq_count() (preempt_count() & HARDIRQ_MASK)
	#define softirq_count() (preempt_count() & SOFTIRQ_MASK)
	#define irq_count() (preempt_count() & (HARDIRQ_MASK \| SOFTIRQ_MASK \
	\| NMI_MASK))

	/*
	* Are we doing bottom half or hardware interrupt processing?
	* Are we in a softirq context? Interrupt context?
	* in_softirq - Are we currently processing softirq or have bh disabled?
	* in_serving_softirq - Are we currently processing softirq?
	*/
	#define in_irq() (hardirq_count())
	#define in_softirq() (softirq_count())
	#define in_interrupt() (irq_count())
	#define in_serving_softirq() (softirq_count() & SOFTIRQ_OFFSET)

	/*
	* Are we in NMI context?
	*/
	#define in_nmi() (preempt_count() & NMI_MASK)

	/*
	* 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_PREEMPT_TRACER)
	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_PREEMPT
	#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_PREEMPT */
	#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_PREEMPT */

	#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(&notifier->link);
	notifier->ops = ops;
	}

	#endif

	#endif /* __LINUX_PREEMPT_H */