4.18-stable review patch. If anyone has any objections, please let me know.
------------------
From: Johannes Berg johannes.berg@intel.com
[ Upstream commit 87915adc3f0acdf03c776df42e308e5a155c19af ]
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@intel.com Signed-off-by: Tejun Heo tj@kernel.org Signed-off-by: Sasha Levin alexander.levin@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- kernel/workqueue.c | 8 ++++++++ 1 file changed, 8 insertions(+)
--- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -2652,6 +2652,9 @@ void flush_workqueue(struct workqueue_st 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_str 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);