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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: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Signed-off-by: Peter 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: bdb4380658 ("sched: Extract the basic add/sub preempt_count modifiers")
Link: http://lkml.kernel.org/r/20150715095204.12246.98268.stgit@buzz
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Konstantin Khlebnikov 2015-07-15 12:52:04 +03:00 committed by Ingo Molnar
parent c56dadf397
commit fe32d3cd5e
5 changed files with 22 additions and 18 deletions
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4
arch/x86/include/asm/preempt.h
View File

@ -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

5
include/asm-generic/preempt.h
View File

@ -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

19
include/linux/preempt.h
View File

@ -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
# 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)

6
include/linux/sched.h
View File

@ -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); \

6
kernel/sched/core.c
View File

@ -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();