linux-kernel - Re: [syzbot] [netfs?] kernel BUG in folio

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Message-ID: <CANp29Y5H3VTZAVZjde5bVRajDUESAnCX+6H1wD90ArpT=EiU3Q@mail.gmail.com>
Date: Wed, 11 Jun 2025 16:08:18 +0200
From: Aleksandr Nogikh <nogikh@...gle.com>
To: Matthew Wilcox <willy@...radead.org>
Cc: syzbot <syzbot+c0dc46208750f063d0e0@...kaller.appspotmail.com>, 
	asmadeus@...ewreck.org, chao@...nel.org, dhowells@...hat.com, hch@....de, 
	hdanton@...a.com, jaegeuk@...nel.org, jlayton@...nel.org, 
	linux-f2fs-devel@...ts.sourceforge.net, linux-fsdevel@...r.kernel.org, 
	linux-kernel@...r.kernel.org, netfs@...ts.linux.dev, 
	syzkaller-bugs@...glegroups.com, v9fs@...ts.linux.dev
Subject: Re: [syzbot] [netfs?] kernel BUG in folio_unlock (3)

On Sun, Jun 1, 2025 at 2:26 AM Matthew Wilcox <willy@...radead.org> wrote:
>
> On Sat, May 31, 2025 at 04:20:02PM -0700, syzbot wrote:
> > syzbot has bisected this issue to:
> >
> > commit 80f31d2a7e5f4efa7150c951268236c670bcb068
> > Author: Christoph Hellwig <hch@....de>
> > Date:   Thu May 8 05:14:32 2025 +0000
>
> That's not possible; this commit is after the original report.
>
> That said, there _is_ a double folio_unlock() in this patch, which
> I'm about to send a fix for.  It's just not fixing the original report.
>

Thanks for bringing this up!
The underlying problem is that syzbot has merged several unrelated
kernel crashes into one bug report (`kernel BUG in folio_unlock` is
just a too generic title). The reported bisection result seems to be
correct, but it refers to only one of those incorrectly merged bugs.

I've just sent a fix for the syzbot's crash report parsing code [1].
It won't affect this specific bug report, but once the new code is
deployed, syzbot will re-report the two underlying findings
separately.

[1] https://github.com/google/syzkaller/pull/6081

-- 
Aleksandr