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Subject[tip:sched/core] sched/wait: Change timeout logic
Commit-ID:  2953ef246b058989657e1e77b36b67566ac06f7b
Gitweb: http://git.kernel.org/tip/2953ef246b058989657e1e77b36b67566ac06f7b
Author: Peter Zijlstra <peterz@infradead.org>
AuthorDate: Wed, 2 Oct 2013 11:22:19 +0200
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Fri, 4 Oct 2013 10:14:44 +0200

sched/wait: Change timeout logic

Commit 4c663cf ("wait: fix false timeouts when using
wait_event_timeout()") introduced an additional condition check after
a timeout but there's a few issues;

- it forgot one site
- it put the check after the main loop; not at the actual timeout
check.

Cure both; by wrapping the condition (as suggested by Oleg), this
avoids double evaluation of 'condition' which could be quite big.

Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20131002092528.028892896@infradead.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
include/linux/wait.h | 24 +++++++++++-------------
1 file changed, 11 insertions(+), 13 deletions(-)

diff --git a/include/linux/wait.h b/include/linux/wait.h
index ccf0c52..b2afd66 100644
--- a/include/linux/wait.h
+++ b/include/linux/wait.h
@@ -179,6 +179,14 @@ wait_queue_head_t *bit_waitqueue(void *, int);
#define wake_up_interruptible_sync_poll(x, m) \
__wake_up_sync_key((x), TASK_INTERRUPTIBLE, 1, (void *) (m))

+#define ___wait_cond_timeout(condition, ret) \
+({ \
+ bool __cond = (condition); \
+ if (__cond && !ret) \
+ ret = 1; \
+ __cond || !ret; \
+})
+
#define __wait_event(wq, condition) \
do { \
DEFINE_WAIT(__wait); \
@@ -217,14 +225,10 @@ do { \
\
for (;;) { \
prepare_to_wait(&wq, &__wait, TASK_UNINTERRUPTIBLE); \
- if (condition) \
+ if (___wait_cond_timeout(condition, ret)) \
break; \
ret = schedule_timeout(ret); \
- if (!ret) \
- break; \
} \
- if (!ret && (condition)) \
- ret = 1; \
finish_wait(&wq, &__wait); \
} while (0)

@@ -299,18 +303,14 @@ do { \
\
for (;;) { \
prepare_to_wait(&wq, &__wait, TASK_INTERRUPTIBLE); \
- if (condition) \
+ if (___wait_cond_timeout(condition, ret)) \
break; \
if (signal_pending(current)) { \
ret = -ERESTARTSYS; \
break; \
} \
ret = schedule_timeout(ret); \
- if (!ret) \
- break; \
} \
- if (!ret && (condition)) \
- ret = 1; \
finish_wait(&wq, &__wait); \
} while (0)

@@ -815,7 +815,7 @@ do { \
\
for (;;) { \
prepare_to_wait(&wq, &__wait, TASK_INTERRUPTIBLE); \
- if (condition) \
+ if (___wait_cond_timeout(condition, ret)) \
break; \
if (signal_pending(current)) { \
ret = -ERESTARTSYS; \
@@ -824,8 +824,6 @@ do { \
spin_unlock_irq(&lock); \
ret = schedule_timeout(ret); \
spin_lock_irq(&lock); \
- if (!ret) \
- break; \
} \
finish_wait(&wq, &__wait); \
} while (0)

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