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author | Tejun Heo <tj@kernel.org> | 2011-11-21 12:32:22 -0800 |
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committer | Tejun Heo <tj@kernel.org> | 2011-11-21 12:32:22 -0800 |
commit | 50fb4f7fc907efff65eadb0b74387a9ffed6e849 (patch) | |
tree | e3392afa49a97c187d7e63f3fee862aef9e342ed /kernel | |
parent | 6fe4c6d466e95d31164f14b1ac4aefb51f0f4f82 (diff) | |
download | linux-50fb4f7fc907efff65eadb0b74387a9ffed6e849.tar.gz linux-50fb4f7fc907efff65eadb0b74387a9ffed6e849.tar.bz2 linux-50fb4f7fc907efff65eadb0b74387a9ffed6e849.zip |
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.c | 8 |
1 files changed, 7 insertions, 1 deletions
diff --git a/kernel/freezer.c b/kernel/freezer.c index 7be56c534397..3f460104a9d6 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); |