At Wed, 3 Dec 2014 18:31:45 +0000, Chris Wilson wrote: > > On Wed, Dec 03, 2014 at 03:45:35PM +0100, Takashi Iwai wrote: > > Hi, > > > > while checking the reported bug about VT switch hang on openSUSE 13.2, > > I also could reproduce a similar issue as reported: namely, X hangs > > when repeatedly switching VT quickly. > > > > For example, running the following on KDE results in the stall of X. > > > > % for i in $(seq 1 100); do chvt 1; chvt 7; done > > > > Looking at the sysrq-t output, it stalls at drm_read(). And after > > putting some debug prints at event handling codes, it shows like: > > > > drm_queue_vblank_event event_space=4064 > > send_vblank_event event_space=4064 > > drm_poll ENTER event_space=4064 > > drm_poll mask=0x41 event_space=4064 > > drm_poll ENTER event_space=4064 > > drm_poll mask=0x41 event_space=4064 > > drm_read ENTER event_space=4064 > > drm_read total=32 event_space=4096 > > drm_poll ENTER event_space=4096 > > drm_poll mask=0x0 event_space=4096 > > drm_read ENTER event_space=4096 > > drm_read ENTER event_space=4096 > > drm_read ENTER event_space=4096 > > > > So, after a vblank event, two poll calls succeeded, followed by one > > drm_read(). After that, there were one poll call without event, > > followed by three(!) drm_read() calls. The last three drm_read() > > never exited, thus X stalled. So, this looks like a race or a > > refcount issue somewhere. > > The key question is how did you get 3 calls to drm_read that each didn't > return? I asked this to myself, too... > The only place where we call drm_read without first doing a poll > is in the WakeupHandler with the drm fd flagged for reads. This is > broken in ZaphodHeads as the drm fd is not O_NONBLOCK without > > commit bd008e5b2953186fc0c6633a885ade95e7043800 > Author: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> > Date: Tue Oct 7 14:13:51 2014 +0100 > > drm: Implement O_NONBLOCK support on /dev/dri/cardN > > I assume that isn't the case as I expect you would have mentioned using > ZaphodHeads. Right, no extra option is used. And, eDP output only. > Maarten found a very similar issue using radeon: > > https://bugs.freedesktop.org/show_bug.cgi?id=77885 > > where the supposition was that the DRM_MASTER was not being > relinquished. Interesting. In the original bug report we've got, the symptom happened at switching two X sessions, as the bfo entry above. http://bugzilla.opensuse.org/show_bug.cgi?id=904097 The reporter mentioned there that his issue was fixed with 3.17.x kernel, so it's likely a different problem from what I've seen. The bug couldn't be reproduced on my machine, so I tried the simple VT quick switches, then hits a new bug now. In anyway, I'll poke a bit more deeply later (maybe on Friday). But, before that, I'd like to ask: can anyone reproduce this problem at all...? thanks, Takashi _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/intel-gfx
