As pointed out by Jarek Poplawski, the patch [WORKQUEUE]: cancel_delayed_work: use del_timer() instead of del_timer_sync() commit: 071b638689464c6b39407025eedd810d5b5e6f5d was wrong, it was merged by mistake after that. From the changelog: after this patch: ... delayed_work_timer_fn->__queue_work() in progress. The latter doesn't differ from the caller's POV, it does make a difference if the caller calls flush_workqueue() after cancel_delayed_work(), in that case flush_workqueue() can miss this work_struct.
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| @@ -160,7 +160,7 @@ static inline int cancel_delayed_work(struct delayed_work *work) · 159 unmodified lines | ||
| 160 | 160 | { |
| 161 | 161 | int ret; |
| 162 | 162 | |
| 163 | − ret = del_timer(&work->timer); | |
| 163 | + ret = del_timer_sync(&work->timer); | |
| 164 | 164 | if (ret) |
| 165 | 165 | work_clear_pending(&work->work); |
| 166 | 166 | return ret; |