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Subject[PATCH pm] freezer: fix wait_event_freezable/__thaw_task races
From: Oleg Nesterov <oleg@redhat.com>

wait_event_freezable() and friends stop the waiting if try_to_freeze()
fails. This is not right, we can race with __thaw_task() and in this
case

- wait_event_freezable() returns the wrong ERESTARTSYS

- wait_event_freezable_timeout() can return the positive
value while condition == F

Change the code to always check __retval/condition before return.

Note: with or without this patch the timeout logic looks strange,
probably we should recalc timeout if try_to_freeze() returns T.

tj: Updated to apply to wait_event_freezekillable() too.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Tejun Heo <tj@kernel.org>
---

So, this should be the last of lost patches. It's on top of

linus/master
+[1] freezer: fix various bugs and simplify implementation, take#2
+[2] usb_storage: don't use set_freezable_with_signal()" + [3]
+[3] freezer: kill unused set_freezable_with_signal()

and available in the following git branch.

git://git.kernel.org/pub/scm/linux/kernel/git/tj/misc.git pm-fix-wait_freezable

Thank you.

[1] http://thread.gmane.org/gmane.linux.kernel/1209247
[2] http://thread.gmane.org/gmane.linux.kernel/1209416
[3] http://thread.gmane.org/gmane.linux.kernel/1209416/focus=1209417

include/linux/freezer.h | 27 ++++++++++++++-------------
1 files changed, 14 insertions(+), 13 deletions(-)

diff --git a/include/linux/freezer.h b/include/linux/freezer.h
index 5f32321..4a1d933 100644
--- a/include/linux/freezer.h
+++ b/include/linux/freezer.h
@@ -113,42 +113,43 @@ static inline int freezer_should_skip(struct task_struct *p)
#define wait_event_freezekillable(wq, condition) \
({ \
int __retval; \
- do { \
+ for (;;) { \
__retval = wait_event_killable(wq, \
(condition) || freezing(current)); \
- if (__retval && !freezing(current)) \
+ if (__retval || (condition)) \
break; \
- else if (!(condition)) \
- __retval = -ERESTARTSYS; \
- } while (try_to_freeze()); \
+ try_to_freeze(); \
+ } \
__retval; \
})

#define wait_event_freezable(wq, condition) \
({ \
int __retval; \
- do { \
+ for (;;) { \
__retval = wait_event_interruptible(wq, \
(condition) || freezing(current)); \
- if (__retval && !freezing(current)) \
+ if (__retval || (condition)) \
break; \
- else if (!(condition)) \
- __retval = -ERESTARTSYS; \
- } while (try_to_freeze()); \
+ try_to_freeze(); \
+ } \
__retval; \
})

-
#define wait_event_freezable_timeout(wq, condition, timeout) \
({ \
long __retval = timeout; \
- do { \
+ for (;;) { \
__retval = wait_event_interruptible_timeout(wq, \
(condition) || freezing(current), \
__retval); \
- } while (try_to_freeze()); \
+ if (__retval <= 0 || (condition)) \
+ break; \
+ try_to_freeze(); \
+ } \
__retval; \
})
+
#else /* !CONFIG_FREEZER */
static inline bool frozen(struct task_struct *p) { return false; }
static inline bool freezing(struct task_struct *p) { return false; }
--
1.7.3.1


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