From: John Ogness <john.ogness@linutronix.de>
To: Petr Mladek <pmladek@suse.com>, Joanne Koong <joannelkoong@gmail.com>
Cc: brauner@kernel.org, djwong@kernel.org,
syzkaller-bugs@googlegroups.com, linux-kernel@vger.kernel.org,
linux-f2fs-devel@lists.sourceforge.net,
linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org,
syzbot <syzbot+3686758660f980b402dc@syzkaller.appspotmail.com>,
jaegeuk@kernel.org,
"amurray@thegoodpenguin.co.uk" <amurray@thegoodpenguin.co.uk>
Subject: Re: [f2fs-dev] [syzbot] [iomap?] kernel BUG in folio_end_read (2)
Date: Wed, 05 Nov 2025 16:00:28 +0106 [thread overview]
Message-ID: <87ldkk34yj.fsf@jogness.linutronix.de> (raw)
In-Reply-To: <aQpFLJM96uRpO4S-@pathway.suse.cz>
On 2025-11-04, Petr Mladek <pmladek@suse.com> wrote:
> Adding John into Cc.
Thanks.
> It rather looks like an internal bug in the printk_ringbuffer code.
> And there is only one recent patch:
>
> https://patch.msgid.link/20250905144152.9137-2-d-tatianin@yandex-team.ru
>
> The scenario leading to the WARN() is not obvious to me. But the patch
> touched this code path. So it is a likely culprit. I have to think
> more about it.
I have been digging into this all day and I can find no explanation.
The patch you refer to brings a minor semantic change: is_blk_wrapped()
returns false if begin_lpos and next_lpos are the same, whereas before
we would have true. However, these values are not allowed to be the same
(except for the data-less special case values).
> Anyway, I wonder if the WARNING is reproducible and if it happens even after
> reverting the commit 67e1b0052f6bb82be84e3 ("printk_ringbuffer: don't
> needlessly wrap data blocks around")
Note that a quick search on lore shows another similar report:
https://lore.kernel.org/all/69078fb6.050a0220.29fc44.0029.GAE@google.com/
We may want to revert the commit until we can take a closer look at
this.
I will divert my energies from code-reading to trying to reproduce this.
John
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WARNING: multiple messages have this Message-ID (diff)
From: John Ogness <john.ogness@linutronix.de>
To: Petr Mladek <pmladek@suse.com>, Joanne Koong <joannelkoong@gmail.com>
Cc: syzbot <syzbot+3686758660f980b402dc@syzkaller.appspotmail.com>,
"amurray@thegoodpenguin.co.uk" <amurray@thegoodpenguin.co.uk>,
brauner@kernel.org, chao@kernel.org, djwong@kernel.org,
jaegeuk@kernel.org, linux-f2fs-devel@lists.sourceforge.net,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-xfs@vger.kernel.org, syzkaller-bugs@googlegroups.com
Subject: Re: [syzbot] [iomap?] kernel BUG in folio_end_read (2)
Date: Wed, 05 Nov 2025 16:00:28 +0106 [thread overview]
Message-ID: <87ldkk34yj.fsf@jogness.linutronix.de> (raw)
In-Reply-To: <aQpFLJM96uRpO4S-@pathway.suse.cz>
On 2025-11-04, Petr Mladek <pmladek@suse.com> wrote:
> Adding John into Cc.
Thanks.
> It rather looks like an internal bug in the printk_ringbuffer code.
> And there is only one recent patch:
>
> https://patch.msgid.link/20250905144152.9137-2-d-tatianin@yandex-team.ru
>
> The scenario leading to the WARN() is not obvious to me. But the patch
> touched this code path. So it is a likely culprit. I have to think
> more about it.
I have been digging into this all day and I can find no explanation.
The patch you refer to brings a minor semantic change: is_blk_wrapped()
returns false if begin_lpos and next_lpos are the same, whereas before
we would have true. However, these values are not allowed to be the same
(except for the data-less special case values).
> Anyway, I wonder if the WARNING is reproducible and if it happens even after
> reverting the commit 67e1b0052f6bb82be84e3 ("printk_ringbuffer: don't
> needlessly wrap data blocks around")
Note that a quick search on lore shows another similar report:
https://lore.kernel.org/all/69078fb6.050a0220.29fc44.0029.GAE@google.com/
We may want to revert the commit until we can take a closer look at
this.
I will divert my energies from code-reading to trying to reproduce this.
John
next prev parent reply other threads:[~2025-11-05 14:54 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-09-18 13:13 [f2fs-dev] [syzbot] [f2fs?] kernel BUG in folio_end_read (2) syzbot
2025-09-18 13:13 ` syzbot
2025-11-01 2:11 ` [f2fs-dev] [syzbot] [iomap?] " syzbot
2025-11-01 2:11 ` syzbot
2025-11-03 16:58 ` [f2fs-dev] " Joanne Koong
2025-11-03 16:58 ` Joanne Koong
2025-11-04 2:43 ` [f2fs-dev] " syzbot
2025-11-04 2:43 ` syzbot
2025-11-04 17:45 ` [f2fs-dev] " Joanne Koong
2025-11-04 17:45 ` Joanne Koong
2025-11-04 18:25 ` [f2fs-dev] " Petr Mladek via Linux-f2fs-devel
2025-11-04 18:25 ` Petr Mladek
2025-11-05 14:54 ` John Ogness [this message]
2025-11-05 14:54 ` John Ogness
2025-11-05 16:49 ` [f2fs-dev] " Petr Mladek via Linux-f2fs-devel
2025-11-05 16:49 ` Petr Mladek
2025-11-05 19:58 ` [f2fs-dev] " John Ogness
2025-11-05 19:58 ` John Ogness
2025-11-06 11:36 ` [f2fs-dev] " John Ogness
2025-11-06 11:36 ` John Ogness
2025-11-06 16:22 ` [f2fs-dev] " Petr Mladek via Linux-f2fs-devel
2025-11-06 16:22 ` Petr Mladek
2025-11-06 18:58 ` [f2fs-dev] " John Ogness
2025-11-06 18:58 ` John Ogness
2025-11-06 19:36 ` [f2fs-dev] " John Ogness
2025-11-06 19:36 ` John Ogness
2025-11-07 11:48 ` [f2fs-dev] " Petr Mladek via Linux-f2fs-devel
2025-11-07 11:48 ` Petr Mladek
2025-11-07 13:41 ` [f2fs-dev] " John Ogness
2025-11-07 13:41 ` John Ogness
2025-11-02 5:39 ` [f2fs-dev] [SPAM] " syzbot
2025-11-02 5:39 ` syzbot
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