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authorTejun Heo <tj@kernel.org>2011-11-21 12:32:22 -0800
committerTejun Heo <tj@kernel.org>2011-11-21 12:32:22 -0800
commit50fb4f7fc907efff65eadb0b74387a9ffed6e849 (patch)
treee3392afa49a97c187d7e63f3fee862aef9e342ed /kernel
parent6fe4c6d466e95d31164f14b1ac4aefb51f0f4f82 (diff)
downloadvexpress-lsk-50fb4f7fc907efff65eadb0b74387a9ffed6e849.tar.gz
freezer: fix current->state restoration race in refrigerator()
refrigerator() saves current->state before entering frozen state and restores it before returning using __set_current_state(); however, this is racy, for example, please consider the following sequence. set_current_state(TASK_INTERRUPTIBLE); try_to_freeze(); if (kthread_should_stop()) break; schedule(); If kthread_stop() races with ->state restoration, the restoration can restore ->state to TASK_INTERRUPTIBLE after kthread_stop() sets it to TASK_RUNNING but kthread_should_stop() may still see zero ->should_stop because there's no memory barrier between restoring TASK_INTERRUPTIBLE and kthread_should_stop() test. This isn't restricted to kthread_should_stop(). current->state is often used in memory barrier based synchronization and silently restoring it w/o mb breaks them. Use set_current_state() instead. Signed-off-by: Tejun Heo <tj@kernel.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/freezer.c8
1 files changed, 7 insertions, 1 deletions
diff --git a/kernel/freezer.c b/kernel/freezer.c
index 7be56c53439..3f460104a9d 100644
--- a/kernel/freezer.c
+++ b/kernel/freezer.c
@@ -58,7 +58,13 @@ void refrigerator(void)
current->flags &= ~PF_FREEZING;
pr_debug("%s left refrigerator\n", current->comm);
- __set_current_state(save);
+
+ /*
+ * Restore saved task state before returning. The mb'd version
+ * needs to be used; otherwise, it might silently break
+ * synchronization which depends on ordered task state change.
+ */
+ set_current_state(save);
}
EXPORT_SYMBOL(refrigerator);