Re: WARNING in cfg80211_connect

On Fri, Oct 2, 2020 at 8:27 AM Johannes Berg [off-list ref] wrote:

On Thu, 2020-10-01 at 21:31 -0700, syzbot wrote:

quoted

syzbot has bisected this issue to:

commit 16d4d43595b4780daac8fcea6d042689124cb094
Author: Christoph Hellwig [off-list ref]
Date:   Wed Jul 20 01:38:55 2016 +0000

    xfs: split direct I/O and DAX path

LOL!

Unlike in many other cases, here I don't even see why it went down that
path. You'd think that Christoph's commit should have no effect
whatsoever, but here we are with syzbot claiming a difference?

I mean, often enough it says something is "caused" by a patch because
that caused e.g. generic netlink family renumbering, or because it
emitted some other ioctl() calls or whatnot that are invalid before and
valid after some other (feature) patch (or vice versa sometimes), but
you'd think that this patch would have _zero_ userspace observable
effect?

Which I guess means that the reproduction of this bug is random, perhaps
timing related.

Hi Johannes,

syzbot provides bisection log which usually answers the why question.
In this case bisection was diverged by an unrelated kernel bug. That's
the most common reason for wrong bisection results. If you are
interested in more reasons for wrong bisection results, some time ago
I did a large analysis of bisection results:
https://groups.google.com/g/syzkaller/c/sR8aAXaWEF4/m/tTWYRgvmAwAJ