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().
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| @@ -2652,6 +2652,9 @@ void flush_workqueue(struct workqueue_struct *wq) · 2651 unmodified lines | |||
| 2652 | if (WARN_ON(!wq_online)) | 2652 | if (WARN_ON(!wq_online)) |
| 2653 | return; | 2653 | return; |
| 2654 | 2654 | ||
| 2655 | lock_map_acquire(&wq->lockdep_map); | ||
| 2656 | lock_map_release(&wq->lockdep_map); | ||
| 2657 | |||
| 2655 | mutex_lock(&wq->mutex); | 2658 | mutex_lock(&wq->mutex); |
| 2656 | 2659 | ||
| 2657 | /* | 2660 | /* |
| @@ -2905,6 +2908,11 @@ static bool __flush_work(struct work_struct *work, bool from_cancel) · 247 unmodified lines | |||
| 2905 | if (WARN_ON(!wq_online)) | 2908 | if (WARN_ON(!wq_online)) |
| 2906 | return false; | 2909 | return false; |
| 2907 | 2910 | ||
| 2911 | if (!from_cancel) { | ||
| 2912 | lock_map_acquire(&work->lockdep_map); | ||
| 2913 | lock_map_release(&work->lockdep_map); | ||
| 2914 | } | ||
| 2915 | |||
| 2908 | if (start_flush_work(work, &barr, from_cancel)) { | 2916 | if (start_flush_work(work, &barr, from_cancel)) { |
| 2909 | wait_for_completion(&barr.done); | 2917 | wait_for_completion(&barr.done); |
| 2910 | destroy_work_on_stack(&barr.work); | 2918 | destroy_work_on_stack(&barr.work); |