Messages in this thread |  | | Date | Tue, 21 Aug 2018 10:55:50 -0700 | From | Tejun Heo <> | Subject | Re: [PATCH 1/2] workqueue: skip lockdep wq dependency in cancel_work_sync() |
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Hello,
On Tue, Aug 21, 2018 at 07:30:21PM +0200, Johannes Berg wrote: > I don't see how? This is only relevant in ordered/single-threaded WQs, > but even there it doesn't matter doesn't matter as explained? > > I'm actually seeing a false positive report from lockdep, because it > *is* flushing, i.e. I'm running into the case of the work actually > running, i.e. the "_sync" part of "cancel_work_sync()" is kicking in, > but in that case a single-threaded WQ can't have anything executing > *before* it, so we don't need to generate a lockdep dependency - and in > fact don't *want* to create one to avoid the false positive. > > 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?
Thanks.
-- tejun
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