From 50fb4f7fc907efff65eadb0b74387a9ffed6e849 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Mon, 21 Nov 2011 12:32:22 -0800 Subject: 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 --- kernel/freezer.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) (limited to 'kernel/freezer.c') 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); -- cgit v1.2.3