On Thu, 10 Jul 2014, Sasha Levin wrote: > On 07/10/2014 03:06 PM, Hugh Dickins wrote: > > On Thu, 10 Jul 2014, Sasha Levin wrote: > >> > On 07/10/2014 02:52 PM, Hugh Dickins wrote: > >>> > > On Thu, 10 Jul 2014, Sasha Levin wrote: > >>>>> > >> > On 07/10/2014 01:55 PM, Hugh Dickins wrote: > >>>>>>>>> > >>>> > >> And finally, (not) holding the i_mmap_mutex: > >>>>>>> > >>> > > I don't understand what prompts you to show this particular > >>>>>>> > >>> > > task. > >>>>>>> > >>> > > I imagine the dump shows lots of other tasks which are > >>>>>>> > >>> > > waiting to get an > >>>>>>> > >>> > > i_mmap_mutex, and quite a lot of other tasks which are > >>>>>>> > >>> > > neither waiting > >>>>>>> > >>> > > for nor holding an i_mmap_mutex. > >>>>>>> > >>> > > > >>>>>>> > >>> > > Why are you showing this one in particular? Because it > >>>>>>> > >>> > > looks like the > >>>>>>> > >>> > > one you fingered yesterday? But I didn't see a good reason > >>>>>>> > >>> > > to finger > >>>>>>> > >>> > > that one either. > >>>>> > >> > > >>>>> > >> > There are a few more tasks like this one, my criteria was tasks > >>>>> > >> > that lockdep > >>>>> > >> > claims were holding i_mmap_mutex, but are actually not. > >>> > > You and Vlastimil enlightened me yesterday that lockdep shows tasks as > >>> > > holding i_mmap_mutex when they are actually waiting to get > >>> > > i_mmap_mutex. > >>> > > Hundreds of those in yesterday's log, hundreds of them in today's. > >> > > >> > What if we move lockdep's acquisition point to after it actually got the > >> > lock? > >> > > >> > We'd miss deadlocks, but we don't care about them right now. Anyways, > >> > doesn't > >> > lockdep have anything built in to allow us to separate between locks > >> > which > >> > we attempt to acquire and locks that are actually acquired? > >> > > >> > (cc PeterZ) > >> > > >> > We can treat locks that are in the process of being acquired the same as > >> > acquired locks to avoid races, but when we print something out it would > >> > be nice to have annotation of the read state of the lock. > > I certainly hope someone can work on improving that. I imagine it would > > be easy, and well worth doing. But won't be looking into it myself. > > I'd be happy to work on that, just want Peter to confirm that there's no > reason > that this is missing right now.
Great, thanks. And for this bug (and many others?) it would also be very helpful if those waiting on a mutex show the current mutex owner's pid. Don't worry about getting a final mergeable patch, covering all lock types: just something hacked up to show that i_mmap_mutex owner would help a lot. But be careful, maybe owner is corrupted, or contains a now-invalid address, or points to something no longer a task_struct. Hugh -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
