workqueue: Catch more locking problems with flush_work()

If a workqueue is flushed with flush_work() lockdep checking can
be circumvented. For example:

 static DEFINE_MUTEX(mutex);

 static void my_work(struct work_struct *w)
 {
         mutex_lock(&mutex);
         mutex_unlock(&mutex);
 }

 static DECLARE_WORK(work, my_work);

 static int __init start_test_module(void)
 {
         schedule_work(&work);
         return 0;
 }
 module_init(start_test_module);

 static void __exit stop_test_module(void)
 {
         mutex_lock(&mutex);
         flush_work(&work);
         mutex_unlock(&mutex);
 }
 module_exit(stop_test_module);

would not always print a warning when flush_work() was called.
In this trivial example nothing could go wrong since we are
guaranteed module_init() and module_exit() don't run concurrently,
but if the work item is schedule asynchronously we could have a
scenario where the work item is running just at the time flush_work()
is called resulting in a classic ABBA locking problem.

Add a lockdep hint by acquiring and releasing the work item
lockdep_map in flush_work() so that we always catch this
potential deadlock scenario.

Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Reviewed-by: Yong Zhang <yong.zhang0@gmail.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Stephen Boyd 2012-04-20 17:28:50 -07:00 committed by Tejun Heo
parent f5b2552b4e
commit 0976dfc1d0

View file

@ -2509,6 +2509,9 @@ bool flush_work(struct work_struct *work)
{
struct wq_barrier barr;
lock_map_acquire(&work->lockdep_map);
lock_map_release(&work->lockdep_map);
if (start_flush_work(work, &barr, true)) {
wait_for_completion(&barr.done);
destroy_work_on_stack(&barr.work);