On Tue, Mar 12, 2019 at 5:08 AM Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote: > > On Mon, Mar 11, 2019 at 08:59:00PM -0700, syzbot wrote: > > syzbot has bisected this bug to: > > > > commit 34e07e42c55aeaa78e93b057a6664e2ecde3fadb > > Author: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> > > Date: Thu Feb 8 10:54:48 2018 +0000 > > > > drm/i915: Add missing kerneldoc for 'ent' in i915_driver_init_early > > > > bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=13220283200000 > > start commit: 34e07e42 drm/i915: Add missing kerneldoc for 'ent' in i915.. > > git tree: upstream > > final crash: https://syzkaller.appspot.com/x/report.txt?x=10a20283200000 > > console output: https://syzkaller.appspot.com/x/log.txt?x=17220283200000 > > kernel config: https://syzkaller.appspot.com/x/.config?x=abc3dc9b7a900258 > > dashboard link: https://syzkaller.appspot.com/bug?extid=1505c80c74256c6118a5 > > userspace arch: amd64 > > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=12c4dc28c00000 > > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=15df4108c00000 > > > > Reported-by: syzbot+1505c80c74256c6118a5@xxxxxxxxxxxxxxxxxxxxxxxxx > > Fixes: 34e07e42 ("drm/i915: Add missing kerneldoc for 'ent' in > > i915_driver_init_early") > > Umm... Might be a good idea to add some plausibility filters - it is, > in theory, possible that adding a line in a comment changes behaviour > (without compiler bugs, even - playing with __LINE__ is all it would > take), but the odds that it's _not_ a false positive are very low. Thanks for pointing this out. I've started collecting all such cases, so that we are able to draw broader conclusions later: https://github.com/google/syzkaller/issues/1051 added for this one: ========= A mix of problems: unrelated bug triggered by the same repro ("WARNING: ODEBUG bug in netdev_freemem"); lots of infrastructure failures ("failed to copy test binary to VM"); also the original failure seems to be flaky. All this contributed to pointing to a random commit. Al Viro points out that the commit only touches comments, so we could mark the end result as suspicious. ========= The infrastructure problems is definitely something we need to fix ("failed to copy test binary to VM") (currently the machine hangs periodically with lots of time consumed by dmcrypt, but I don't know if it's related or not yet). Re the comment-only changes, I would like to see more cases where it would help before we start creating new universes for this. We could parse sources with clang to understand that a change was comment-only, but I guess kernel is mostly broken with clang throughout history....
