[PATCH 3.14 25/25] sched/preempt: Fix cond_resched_lock() and cond_resched_softirq()

Greg Kroah-Hartman
2015-10-23T18:11:07Z

From: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>

commit fe32d3cd5e8eb0f82e459763374aa80797023403 upstream.

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: bdb438065890 ("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>
Signed-off-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/x86/include/asm/preempt.h | 4 ++--
include/asm-generic/preempt.h | 5 +++--
include/linux/preempt.h | 5 +++--
include/linux/preempt_mask.h | 14 +++++++++++---
include/linux/sched.h | 6 ------
kernel/sched/core.c | 6 +++---
6 files changed, 22 insertions(+), 18 deletions(-)

--- a/arch/x86/include/asm/preempt.h
+++ b/arch/x86/include/asm/preempt.h
@@ -105,9 +105,9 @@ static __always_inline bool __preempt_co
/*
* 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(!__this_cpu_read_4(__preempt_count));
+ return unlikely(__this_cpu_read_4(__preempt_count) == preempt_offset);
}

#ifdef CONFIG_PREEMPT
--- a/include/asm-generic/preempt.h
+++ b/include/asm-generic/preempt.h
@@ -74,9 +74,10 @@ static __always_inline bool __preempt_co
/*
* 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
--- a/include/linux/preempt.h
+++ b/include/linux/preempt.h
@@ -22,7 +22,8 @@
#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)
@@ -61,7 +62,7 @@ do { \

#define preempt_check_resched() \
do { \
- if (should_resched()) \
+ if (should_resched(0)) \
__preempt_schedule(); \
} while (0)

--- a/include/linux/preempt_mask.h
+++ b/include/linux/preempt_mask.h
@@ -71,13 +71,21 @@
*/
#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:
*
* spin_lock_bh()
@@ -90,7 +98,7 @@
*
* 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
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2647,12 +2647,6 @@ 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); \
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4113,7 +4113,7 @@ static void __cond_resched(void)

int __sched _cond_resched(void)
{
- if (should_resched()) {
+ if (should_resched(0)) {
__cond_resched();
return 1;
}
@@ -4131,7 +4131,7 @@ 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);
@@ -4153,7 +4153,7 @@ int __sched __cond_resched_softirq(void)
{
BUG_ON(!in_softirq());

- if (should_resched()) {
+ if (should_resched(SOFTIRQ_DISABLE_OFFSET)) {
local_bh_enable();
__cond_resched();
local_bh_disable();