[PATCH 2/2] workqueue: create lockdep dependency in flush_work()

From: Johannes Berg <redacted>

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.

Signed-off-by: Johannes Berg <redacted>
---
 kernel/workqueue.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index a6c2b823f348..29d4d84ba512 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c

@@ -2852,6 +2852,11 @@ static bool start_flush_work(struct work_struct *work, struct wq_barrier *barr,
 
 	might_sleep();
 
+	if (!from_cancel) {
+		lock_map_acquire(&work->lockdep_map);
+		lock_map_release(&work->lockdep_map);
+	}
+
 	local_irq_disable();
 	pool = get_work_pool(work);
 	if (!pool) {

-- 
2.14.4