Messages in this thread | | | Date | Fri, 20 Apr 2012 16:32:02 +0800 | From | Yong Zhang <> | Subject | Re: [PATCH 1/2] workqueue: Catch more locking problems with flush_work() |
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On Fri, Apr 20, 2012 at 01:18:19AM -0700, Stephen Boyd wrote: > On 4/20/2012 12:18 AM, Yong Zhang wrote: > > On Thu, Apr 19, 2012 at 11:26:47PM -0700, Stephen Boyd wrote: > >> complain in the case where the work is not queued. That case is not a > >> false positive. We will get a lockdep warning if the work is running > > IIRC, flush_work() is just a nop when a work is not queued nor running. > > Agreed, but it's better to always print a lockdep warning instead of > only when the deadlock is going to occur.
It will IMHO.
> > > > >> (when start_flush_work() returns true) solely with the > >> lock_map_acquire() on cwq->wq->lockdep_map. > > Yeah, that is the point we use lockdep to detect deadlock for workqueue. > > > > But when looking at start_flush_work(), for some case > > !(cwq->wq->saved_max_active == 1 || cwq->wq->flags & WQ_RESCUER), > > lock_map_acquire_read() is called, but recursive read is not added to > > the chain list. So when lock_map_acquire_read(&cwq->wq->lockdep_map) > > is called, deadlock will not be detected. I hope you don't hit that > > special case. > > Hmm. Originally I had what you suggested in my patch but I left it out > because I wasn't sure if it would cause false positives. > Do you see any > possibility for false positives?
No, I don't. My test indeed show nothing (just build and boot).
>I'll add it back in if not.
It's great if you can try it :)
Thanks, Yong
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