From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 496CE32145E; Wed, 5 Nov 2025 14:54:30 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=193.142.43.55 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762354472; cv=none; b=j/ulP0OE9pnEs/znBp5+pu6I+lE8FkOXuzRJFt607z1P4iZKpRDoh+npxs5VgJWlAw4ytaQZN+mX2c3DWG7l5nRJ7cMfktS2yQgxpnyMfQnCYnoGAg2yTpADzjfvMdcQlDCgrsC0MvTYhBT4e7zjj4tvf0lNSitzIpVrLeX52PQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762354472; c=relaxed/simple; bh=wg6hvq1fDEKKHo+ksANPIzinuZ9SiV9KbZGzhCFjZa4=; h=From:To:Cc:Subject:In-Reply-To:References:Date:Message-ID: MIME-Version:Content-Type; b=k9yX+fOEw4IWS7ZB18LhlbUYaFA2CrstnZ1FotGIeSr+OLabvCbXZ3sE1UajNeqF3/JYpEX0xF53S155t27EfUhXiEEjdZcoGJJ5YbmjD/BicNO99fMtv7aJeyuww6Qum4RRdYym0+JWm/sfev5+gJw6/obzYUQ9yyM8kMmdgR8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de; spf=pass smtp.mailfrom=linutronix.de; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=ixdPaQRV; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=2m96Jera; arc=none smtp.client-ip=193.142.43.55 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linutronix.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="ixdPaQRV"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="2m96Jera" From: John Ogness DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1762354469; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=4WxYZ+JeksWx9qzLRbdr/qx4v36wWsQth6BFNnfgxlQ=; b=ixdPaQRVOB+Vf/Rjjt9TIHFHfrqbSTg3oXt1SBrY/0vcLZ3MY87d7ex88vzn9l3lEIuIr4 SYOhn1zLfUUR9JxPwjeVT3ocT2rGfFH9s0+WhzF8+55J3QdyYj0GGo9OxBGtgCLzc3cEB4 j+7huapGfATu6aXcGZx3HvIVIRJd2rx361EYoZ4iWJww4qISDNV+YhQMhfuIfwD9zpD4EU 0vfvDqS4xB2aOQCu29sG8SGr4nzHqkpKmfxGlwBIaWjcQXMCYgdpWNJH4BD4eRd+S5GU80 LcUK6NbiRXQLTibQHLucRQq7kjLOW/8GAhso1ChYyGhbENo+5sYW9hDGQAAu6A== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1762354469; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=4WxYZ+JeksWx9qzLRbdr/qx4v36wWsQth6BFNnfgxlQ=; b=2m96Jera/0TPmblmwvx8TPXahXVuSgKJFttdj9F8sJkbbeCoeN5f4LoITxROKlrWQVRSFQ 9nPJhdCcdzIbFODw== To: Petr Mladek , Joanne Koong Cc: syzbot , "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) In-Reply-To: References: <69096836.a70a0220.88fb8.0006.GAE@google.com> Date: Wed, 05 Nov 2025 16:00:28 +0106 Message-ID: <87ldkk34yj.fsf@jogness.linutronix.de> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain On 2025-11-04, Petr Mladek 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