Re: [f2fs-dev] [syzbot] [netfs?] kernel BUG in folio_unlock (3)

Re: [f2fs-dev] [syzbot] [netfs?] kernel BUG in folio_unlock (3)

[syzbot]

syzbot has bisected this issue to:

commit 80f31d2a7e5f4efa7150c951268236c670bcb068
Author: Christoph Hellwig <hch@lst.de>
Date:   Thu May 8 05:14:32 2025 +0000

    f2fs: return bool from __write_node_folio

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=1129d00c580000
start commit:   0f70f5b08a47 Merge tag 'pull-automount' of git://git.kerne..
git tree:       upstream
final oops:     https://syzkaller.appspot.com/x/report.txt?x=1329d00c580000
console output: https://syzkaller.appspot.com/x/log.txt?x=1529d00c580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=22765942f2e2ebcf
dashboard link: https://syzkaller.appspot.com/bug?extid=c0dc46208750f063d0e0
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=15bfe970580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=13bfe970580000

Reported-by: syzbot+c0dc46208750f063d0e0@syzkaller.appspotmail.com
Fixes: 80f31d2a7e5f ("f2fs: return bool from __write_node_folio")

For information about bisection process see: https://goo.gl/tpsmEJ#bisection


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Re: [f2fs-dev] [syzbot] [netfs?] kernel BUG in folio_unlock (3)

[Matthew Wilcox]

On Sat, May 31, 2025 at 04:20:02PM -0700, syzbot wrote:
> syzbot has bisected this issue to:
> 
> commit 80f31d2a7e5f4efa7150c951268236c670bcb068
> Author: Christoph Hellwig <hch@lst.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.


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Re: [f2fs-dev] [syzbot] [netfs?] kernel BUG in folio_unlock (3)

[Aleksandr Nogikh via Linux-f2fs-devel]

On Sun, Jun 1, 2025 at 2:26 AM Matthew Wilcox <willy@infradead.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@lst.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


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