Messages in this thread | | | Subject | Re: [PATCH 1/2] workqueue: skip lockdep wq dependency in cancel_work_sync() | From | Johannes Berg <> | Date | Tue, 21 Aug 2018 21:20:41 +0200 |
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On Tue, 2018-08-21 at 10:55 -0700, Tejun Heo wrote:
> > I'm not really sure what you think we might be missing? Am I missing > > some case where cancel_work_sync() can possibly deadlock? Apart from the > > issue I addressed in the second patch, obviously. > > Ah, that was me being slow. I thought you were skipping the work's > lockdep_map. I can almost swear we had that before (the part you're > adding on the second patch). Right, fd1a5b04dfb8 ("workqueue: Remove > now redundant lock acquisitions wrt. workqueue flushes") removed it > because it gets propagated through wait_for_completion(). Did we miss > some cases with that change?
Hmm.
It doesn't seem to be working.
No, ok, actually it probably *does*, but the point is similar to my issue # 3 before - we don't do any of this unless the work is actually running, but we really want the lockdep annotation *regardless* of that, so that we catch the error unconditionally.
So perhaps that commit just needs to be reverted entirely - I'd only looked at a small subset of it, but the flush_workqueue() case has the same problem - we only get to the completion when there's something to flush, not when the workqueue happens to actually be empty. But again, for lockdep we want to catch *potential* problems, not only *actual* ones.
The remaining part of the patch I'm not sure I fully understand (removal of lockdep_init_map_crosslock()), but I suppose if we revert the other bits we need to revert this as well.
So please drop this patch, but revert Byungchul Park's commit fd1a5b04dfb8 again, I don't think the lockdep annotations there are really redundant as I just explained.
johannes
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