On Fri, Aug 20, 2021 at 9:23 PM Thomas Zimmermann <tzimmermann@xxxxxxx> wrote: > Hi > > Am 20.08.21 um 17:45 schrieb syzbot: > > syzbot has bisected this issue to: > > Good bot! > > > > > commit ea40d7857d5250e5400f38c69ef9e17321e9c4a2 > > Author: Daniel Vetter <daniel.vetter@xxxxxxxx> > > Date: Fri Oct 9 23:21:56 2020 +0000 > > > > drm/vkms: fbdev emulation support > > Here's a guess. > > GEM SHMEM + fbdev emulation requires that > (drm_mode_config.prefer_shadow_fbdev = true). Otherwise, deferred I/O > and SHMEM conflict over the use of page flags IIRC. But we should only set up defio if fb->dirty is set, which vkms doesn't do. So there's something else going on? So there must be something else funny going on here I think ... No idea what's going on really. -Daniel > From a quick grep, vkms doesn't set prefer_shadow_fbdev and an alarming > amount of SHMEM-based drivers don't do either. > > Best regards > Thomas > > > > > bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=11c31d55300000 > > start commit: 614cb2751d31 Merge tag 'trace-v5.14-rc6' of git://git.kern.. > > git tree: upstream > > final oops: https://syzkaller.appspot.com/x/report.txt?x=13c31d55300000 > > console output: https://syzkaller.appspot.com/x/log.txt?x=15c31d55300000 > > kernel config: https://syzkaller.appspot.com/x/.config?x=96f0602203250753 > > dashboard link: https://syzkaller.appspot.com/bug?extid=91525b2bd4b5dff71619 > > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=122bce0e300000 > > > > Reported-by: syzbot+91525b2bd4b5dff71619@xxxxxxxxxxxxxxxxxxxxxxxxx > > Fixes: ea40d7857d52 ("drm/vkms: fbdev emulation support") > > > > For information about bisection process see: https://goo.gl/tpsmEJ#bisection > > > > -- > Thomas Zimmermann > Graphics Driver Developer > SUSE Software Solutions Germany GmbH > Maxfeldstr. 5, 90409 Nürnberg, Germany > (HRB 36809, AG Nürnberg) > Geschäftsführer: Felix Imendörffer > -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch
