4.18-stable review patch. If anyone has any objections, please let me know.
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From: Johannes Berg johannes.berg@intel.com
[ Upstream commit d6e89786bed977f37f55ffca11e563f6d2b1e3b5 ]
In cancel_work_sync(), we can only have one of two cases, even with an ordered workqueue: * the work isn't running, just cancelled before it started * the work is running, but then nothing else can be on the workqueue before it
Thus, we need to skip the lockdep workqueue dependency handling, otherwise we get false positive reports from lockdep saying that we have a potential deadlock when the workqueue also has other work items with locking, e.g.
work1_function() { mutex_lock(&mutex); ... } work2_function() { /* nothing */ }
other_function() { queue_work(ordered_wq, &work1); queue_work(ordered_wq, &work2); mutex_lock(&mutex); cancel_work_sync(&work2); }
As described above, this isn't a problem, but lockdep will currently flag it as if cancel_work_sync() was flush_work(), which *is* a problem.
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 | 37 ++++++++++++++++++++++--------------- 1 file changed, 22 insertions(+), 15 deletions(-)
--- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -2843,7 +2843,8 @@ reflush: } EXPORT_SYMBOL_GPL(drain_workqueue);
-static bool start_flush_work(struct work_struct *work, struct wq_barrier *barr) +static bool start_flush_work(struct work_struct *work, struct wq_barrier *barr, + bool from_cancel) { struct worker *worker = NULL; struct worker_pool *pool; @@ -2885,7 +2886,8 @@ static bool start_flush_work(struct work * workqueues the deadlock happens when the rescuer stalls, blocking * forward progress. */ - if (pwq->wq->saved_max_active == 1 || pwq->wq->rescuer) { + if (!from_cancel && + (pwq->wq->saved_max_active == 1 || pwq->wq->rescuer)) { lock_map_acquire(&pwq->wq->lockdep_map); lock_map_release(&pwq->wq->lockdep_map); } @@ -2896,6 +2898,22 @@ already_gone: return false; }
+static bool __flush_work(struct work_struct *work, bool from_cancel) +{ + struct wq_barrier barr; + + if (WARN_ON(!wq_online)) + return false; + + if (start_flush_work(work, &barr, from_cancel)) { + wait_for_completion(&barr.done); + destroy_work_on_stack(&barr.work); + return true; + } else { + return false; + } +} + /** * flush_work - wait for a work to finish executing the last queueing instance * @work: the work to flush @@ -2909,18 +2927,7 @@ already_gone: */ bool flush_work(struct work_struct *work) { - struct wq_barrier barr; - - if (WARN_ON(!wq_online)) - return false; - - if (start_flush_work(work, &barr)) { - wait_for_completion(&barr.done); - destroy_work_on_stack(&barr.work); - return true; - } else { - return false; - } + return __flush_work(work, false); } EXPORT_SYMBOL_GPL(flush_work);
@@ -2986,7 +2993,7 @@ static bool __cancel_work_timer(struct w * isn't executing. */ if (wq_online) - flush_work(work); + __flush_work(work, true);
clear_work_data(work);