Messages in this thread Patch in this message | | | From | Tejun Heo <> | Subject | [PATCH 01/17] freezer: fix current->state restoration race in refrigerator() | Date | Mon, 31 Oct 2011 12:05:12 -0700 |
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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> --- kernel/freezer.c | 8 +++++++- 1 files changed, 7 insertions(+), 1 deletions(-)
diff --git a/kernel/freezer.c b/kernel/freezer.c index 66a594e..19a20b2 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); -- 1.7.3.1
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