From: Daniel Vetter <daniel.vetter@ffwll.ch>
To: Thomas Zimmermann <tzimmermann@suse.de>
Cc: syzbot <syzbot+91525b2bd4b5dff71619@syzkaller.appspotmail.com>,
"Dave Airlie" <airlied@linux.ie>,
"Christian König" <christian.koenig@amd.com>,
"Daniel Vetter" <daniel.vetter@intel.com>,
dri-devel <dri-devel@lists.freedesktop.org>,
linaro-mm-sig-owner@lists.linaro.org,
"moderated list:DMA BUFFER SHARING FRAMEWORK"
<linaro-mm-sig@lists.linaro.org>,
"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
"open list:DMA BUFFER SHARING FRAMEWORK"
<linux-media@vger.kernel.org>,
"Maarten Lankhorst" <maarten.lankhorst@linux.intel.com>,
"Melissa Wen" <melissa.srw@gmail.com>,
"Maxime Ripard" <mripard@kernel.org>,
"Sumit Semwal" <sumit.semwal@linaro.org>,
syzkaller-bugs <syzkaller-bugs@googlegroups.com>
Subject: Re: [syzbot] WARNING in drm_gem_shmem_vm_open
Date: Fri, 20 Aug 2021 21:33:16 +0200 [thread overview]
Message-ID: <CAKMK7uEP_PNr1uDV_FeH2-Q9oGGsr3ux2rpkXHrJpPG=hOaf=Q@mail.gmail.com> (raw)
In-Reply-To: <dc7ca5ae-afc1-f840-8dfc-3f2361cd4360@suse.de>
On Fri, Aug 20, 2021 at 9:23 PM Thomas Zimmermann <tzimmermann@suse.de> 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@ffwll.ch>
> > 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@syzkaller.appspotmail.com
> > 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
next prev parent reply other threads:[~2021-08-20 19:33 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-19 8:21 [syzbot] WARNING in drm_gem_shmem_vm_open syzbot
2021-08-20 15:45 ` syzbot
2021-08-20 19:23 ` Thomas Zimmermann
2021-08-20 19:33 ` Daniel Vetter [this message]
2022-01-31 7:50 ` syzbot
2022-05-12 13:10 ` Dmitry Vyukov
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