From: Oleg Nesterov <oleg@redhat.com>
Date: Wed, 23 Nov 2011 17:28:17 +0000 (-0800)
Subject: freezer: fix wait_event_freezable/__thaw_task races
X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=24b7ead3fb0bae267c2ee50898eb4c13aedd1e9f;p=linux-beck.git

freezer: fix wait_event_freezable/__thaw_task races

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.

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

diff --git a/include/linux/freezer.h b/include/linux/freezer.h
index a33550fc05c5..09570ac22be6 100644
--- a/include/linux/freezer.h
+++ b/include/linux/freezer.h
@@ -122,28 +122,30 @@ static inline int freezer_should_skip(struct task_struct *p)
 #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; }