On Mon, May 18, 2015 at 10:30:06AM +0200, Daniel Vetter wrote: > On Fri, May 15, 2015 at 12:09:00PM +0100, Tvrtko Ursulin wrote: > > > > Hi, > > > > On 05/15/2015 11:42 AM, Chris Wilson wrote: > > >Mika encountered one pathological scenario under X where acquiring all > > >the mm locks (required to insert a mmu notifier) was very slow, so slow > > >that by the time we tried to lock the struct_mutex with the usual call > > >to i915_mutex_lock_interruptible(), X's signal timer had fired causing > > >us to restart the ioctl (and so looped indefinitely). > > > > Indefinite loop? Are you saying userptr creation endlessly fails to manages > > to finish in 10ms (or is it even 100ms, forgot what timer Xorg setups up)? > > The __mmu_notifier_register call? Yes. In this scenario it is taking longer than 100ms to take all the mm locks. I presume it is simply due to there being a vast number of mm on Mika's machine. > > >While I suspect this is the result of another bug (something leaking mm > > >perhaps?) we can forgo the error checking and interuptible nature of the > > >lock here so we only have to pay the expense once and get on with it. > > >This does expose the userptr creation routine to a driver livelock > > >though by not being interruptible. > > > > How is this acceptable then if it can live-lock? How does that happen? > > If the i915 driver somehow dies it's a lot nicer for the user to be able > to hit ^C and get out of trouble again and debug further than make > anything touching i915 be stuck forever. > > But I think this is a justified exception. Queued for -next, thanks for > the patch. Oops, gcc didn't warn about ret being used uninitialized. I guess I am used to using it as a crutch. -Chris -- Chris Wilson, Intel Open Source Technology Centre _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/intel-gfx
