From: Johannes Berg <johannes.berg@xxxxxxxxx>
In flush_work(), we need to create a lockdep dependency so that
the following scenario is appropriately tagged as a problem:
work_function()
{
mutex_lock(&mutex);
...
}
other_function()
{
mutex_lock(&mutex);
flush_work(&work); // or cancel_work_sync(&work);
}
This is a problem since the work might be running and be blocked
on trying to acquire the mutex.
Similarly, in flush_workqueue().
These were removed after cross-release partially caught these
problems, but now cross-release was reverted anyway. IMHO the
removal was erroneous anyway though, since lockdep should be
able to catch potential problems, not just actual ones, and
cross-release would only have caught the problem when actually
invoking wait_for_completion().
Fixes: fd1a5b04dfb8 ("workqueue: Remove now redundant lock acquisitions wrt. workqueue flushes")
Signed-off-by: Johannes Berg <johannes.berg@xxxxxxxxx>
---
kernel/workqueue.c | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index a6c2b823f348..60e80198c3df 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -2652,6 +2652,9 @@ void flush_workqueue(struct workqueue_struct *wq)
if (WARN_ON(!wq_online))
return;
+ lock_map_acquire(&wq->lockdep_map);
+ lock_map_release(&wq->lockdep_map);
+
mutex_lock(&wq->mutex);
/*
@@ -2905,6 +2908,11 @@ static bool __flush_work(struct work_struct *work, bool from_cancel)
if (WARN_ON(!wq_online))
return false;
+ if (!from_cancel) {
+ lock_map_acquire(&work->lockdep_map);
+ lock_map_release(&work->lockdep_map);
+ }
+
if (start_flush_work(work, &barr, from_cancel)) {
wait_for_completion(&barr.done);
destroy_work_on_stack(&barr.work);
--
2.14.4
