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Commit fe32d3cd authored by Konstantin Khlebnikov's avatar Konstantin Khlebnikov Committed by Ingo Molnar
Browse files

sched/preempt: Fix cond_resched_lock() and cond_resched_softirq() 



These functions check should_resched() before unlocking spinlock/bh-enable:
preempt_count always non-zero => should_resched() always returns false.
cond_resched_lock() worked iff spin_needbreak is set.

This patch adds argument "preempt_offset" to should_resched().

preempt_count offset constants for that:

  PREEMPT_DISABLE_OFFSET  - offset after preempt_disable()
  PREEMPT_LOCK_OFFSET     - offset after spin_lock()
  SOFTIRQ_DISABLE_OFFSET  - offset after local_bh_distable()
  SOFTIRQ_LOCK_OFFSET     - offset after spin_lock_bh()

Signed-off-by: default avatarKonstantin Khlebnikov <khlebnikov@yandex-team.ru>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Alexander Graf <agraf@suse.de>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: David Vrabel <david.vrabel@citrix.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: bdb43806 ("sched: Extract the basic add/sub preempt_count modifiers")
Link: http://lkml.kernel.org/r/20150715095204.12246.98268.stgit@buzz


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent c56dadf3

arch/x86/include/asm/preempt.h

+2 −2
Original line number Diff line number Diff line
@@ -90,9 +90,9 @@ static __always_inline bool __preempt_count_dec_and_test(void) 
/*

 * Returns true when we need to resched and can (barring IRQ state).

 */

static __always_inline bool should_resched(void)

static __always_inline bool should_resched(int preempt_offset)

{

	return unlikely(!raw_cpu_read_4(__preempt_count));

	return unlikely(raw_cpu_read_4(__preempt_count) == preempt_offset);

}



#ifdef CONFIG_PREEMPT

include/asm-generic/preempt.h

+3 −2
Original line number Diff line number Diff line
@@ -71,9 +71,10 @@ static __always_inline bool __preempt_count_dec_and_test(void) 
/*

 * Returns true when we need to resched and can (barring IRQ state).

 */

static __always_inline bool should_resched(void)

static __always_inline bool should_resched(int preempt_offset)

{

	return unlikely(!preempt_count() && tif_need_resched());

	return unlikely(preempt_count() == preempt_offset &&

			tif_need_resched());

}



#ifdef CONFIG_PREEMPT

include/linux/preempt.h

+14 −5
Original line number Diff line number Diff line
@@ -84,12 +84,20 @@ 
 */

#define in_nmi()	(preempt_count() & NMI_MASK)



/*

 * The preempt_count offset after preempt_disable();

 */

#if defined(CONFIG_PREEMPT_COUNT)

# define PREEMPT_DISABLE_OFFSET 1

# 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:

 *
@@ -103,7 +111,7 @@ 
 *

 * Work as expected.

 */

#define SOFTIRQ_LOCK_OFFSET (SOFTIRQ_DISABLE_OFFSET + PREEMPT_DISABLE_OFFSET)

#define SOFTIRQ_LOCK_OFFSET (SOFTIRQ_DISABLE_OFFSET + PREEMPT_LOCK_OFFSET)



/*

 * Are we running in atomic context?  WARNING: this macro cannot
@@ -124,7 +132,8 @@ 
#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(); })

#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)
@@ -184,7 +193,7 @@ do { \ 


#define preempt_check_resched() \

do { \

	if (should_resched()) \

	if (should_resched(0)) \

		__preempt_schedule(); \

} while (0)

include/linux/sched.h

+0 −6
Original line number Diff line number Diff line
@@ -2891,12 +2891,6 @@ extern int _cond_resched(void); 


extern int __cond_resched_lock(spinlock_t *lock);



#ifdef CONFIG_PREEMPT_COUNT

#define PREEMPT_LOCK_OFFSET	PREEMPT_OFFSET

#else

#define PREEMPT_LOCK_OFFSET	0

#endif



#define cond_resched_lock(lock) ({				\

	___might_sleep(__FILE__, __LINE__, PREEMPT_LOCK_OFFSET);\

	__cond_resched_lock(lock);				\

kernel/sched/core.c

+3 −3
Original line number Diff line number Diff line
@@ -4496,7 +4496,7 @@ SYSCALL_DEFINE0(sched_yield) 


int __sched _cond_resched(void)

{

	if (should_resched()) {

	if (should_resched(0)) {

		preempt_schedule_common();

		return 1;

	}
@@ -4514,7 +4514,7 @@ EXPORT_SYMBOL(_cond_resched); 
 */

int __cond_resched_lock(spinlock_t *lock)

{

	int resched = should_resched();

	int resched = should_resched(PREEMPT_LOCK_OFFSET);

	int ret = 0;



	lockdep_assert_held(lock);
@@ -4536,7 +4536,7 @@ int __sched __cond_resched_softirq(void) 
{

	BUG_ON(!in_softirq());



	if (should_resched()) {

	if (should_resched(SOFTIRQ_DISABLE_OFFSET)) {

		local_bh_enable();

		preempt_schedule_common();

		local_bh_disable();