Re: INFO: task hung in fb_open

From: Dmitry Vyukov <dvyukov@google.com>
To: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: syzbot <syzbot+a4ae1442ccc637162dc1@syzkaller.appspotmail.com>,
	Dave Airlie <airlied@linux.ie>,
	Ayan Kumar Halder <ayan.halder@arm.com>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>,
	dri-devel <dri-devel@lists.freedesktop.org>,
	Gerd Hoffmann <kraxel@redhat.com>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	Linux Fbdev development list <linux-fbdev@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
	Maxime Ripard <maxime.ripard@bootlin.com>,
	Peter Rosin <peda@axentia.se>, Sam Ravnborg <sam@ravnborg.org>,
	syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
	"Syrjala, Ville" <ville.syrjala@linux.intel.com>,
	Chen-Yu Tsai <wens@csie.org>
Subject: Re: INFO: task hung in fb_open
Date: Thu, 5 Dec 2019 17:45:22 +0100	[thread overview]
Message-ID: <CACT4Y+ZjQSvpZAnLkp6w8erqtraZGkXB2O84BFmcRN_Rm6fs3Q@mail.gmail.com> (raw)
In-Reply-To: <CAKMK7uF4AR_tRxt5wBKxzz6gTPJmub3A=xyuh1HjgvfYy7RCBg@mail.gmail.com>

On Thu, Dec 5, 2019 at 3:05 PM Daniel Vetter <daniel.vetter@ffwll.ch> wrote:
>
> On Thu, Dec 5, 2019 at 2:38 PM syzbot
> <syzbot+a4ae1442ccc637162dc1@syzkaller.appspotmail.com> wrote:
> >
> > syzbot has bisected this bug to:
> >
> > commit 979c11ef39cee79d6f556091a357890962be2580
> > Author: Ayan Kumar Halder <ayan.halder@arm.com>
> > Date:   Tue Jul 17 17:13:46 2018 +0000
> >
> >      drm/sun4i: Substitute sun4i_backend_format_is_yuv() with format->is_yuv
>
> Pretty sure your GCD machine is not using the sun4i driver. It's also
> very far away from the code that's blowing up. bisect gone wrong?
> -Daniel

Yes, this driver is not even enabled in the config.
I see 2 issues with kernel in the bisect log:
1. Unrelated machine hangs get in the way of bisection process (or
that "no output" another manifestation of this bug?).
2. Somehow this change to not compiled file changed vmlinux thus
detection of unrelated changes failed. Non-deterministic kernel builds
issue is tracked here:
https://github.com/google/syzkaller/issues/1271#issuecomment-559093018
but so far I don't have any glues/ideas.

> > bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=15d2f97ee00000
> > start commit:   596cf45c Merge branch 'akpm' (patches from Andrew)
> > git tree:       upstream
> > console output: https://syzkaller.appspot.com/x/log.txt?x=13d2f97ee00000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=7d8ab2e0e09c2a82
> > dashboard link: https://syzkaller.appspot.com/bug?extid=a4ae1442ccc637162dc1
> > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=14273edae00000
> > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=15e7677ae00000
> >
> > Reported-by: syzbot+a4ae1442ccc637162dc1@syzkaller.appspotmail.com
> > Fixes: 979c11ef39ce ("drm/sun4i: Substitute sun4i_backend_format_is_yuv()
> > with format->is_yuv")
> >
> > For information about bisection process see: https://goo.gl/tpsmEJ#bisection
>
>
>
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> +41 (0) 79 365 57 48 - http://blog.ffwll.ch
>
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