Hi, > On Tue, Aug 21, 2018 at 07:18:14PM +0200, Johannes Berg wrote: > > > But this can lead to a deadlock. I'd much rather err on the side of > > > discouraging complex lock dancing around ordered workqueues, no? > > > > What can lead to a deadlock? > > Oh not this particular case, but I was wondering whether we'd be > missing legitimate possible deadlock cases by skipping lockdep for all > cancel_work_sync()'s as they can actually flush. 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. johannes
