From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail3-167.sinamail.sina.com.cn (mail3-167.sinamail.sina.com.cn [202.108.3.167]) (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 C65BD13D886 for ; Tue, 14 Jul 2026 04:38:56 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=202.108.3.167 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784003940; cv=none; b=K4Mez+fM8CSvXQ79DJotwLJaaC8CZ3e1svD99PJqrSs7tGBhSb9EsrRV427m9FHVuZrpunaGEiRq4C7XgF7Wn+QrmfmQbGAkfEMh5FyNdUe+h8oVyYaYmkCa1VKHYqCzCjJlU0jpQRuaBedbOD9kaf5TvfPQtkQhat+lFYssGIY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784003940; c=relaxed/simple; bh=63iCjLzjUGgIPWgpXrZGHZFDsLVx5r5fTToGdyRWLC4=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=K7Xe7r3DelfmsuPbWtUQV0uZ4+6s/ieTQWrJArYFoaoKNnJFPVGYEWq5XRYcpGzaVEmj2WAksKz3UUT1aNTBn0+gqANrv4au+fdu1oafI/2NZGwVMGIyapnq6KhdHVa1GG0i//G7ufNDjAm/Tv3uMPOrqWzNaEgBLRiNOYBk24c= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=sina.com; spf=pass smtp.mailfrom=sina.com; dkim=pass (1024-bit key) header.d=sina.com header.i=@sina.com header.b=IaTzZsK7; arc=none smtp.client-ip=202.108.3.167 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=sina.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=sina.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=sina.com header.i=@sina.com header.b="IaTzZsK7" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=sina.com; s=201208; t=1784003937; bh=E+DqH9w0CFDT+FpgETLE+ky0m/kkR8WsjPHPbAseKBI=; h=From:Subject:Date:Message-ID; b=IaTzZsK7OLSdN8/jQwtyffRKZ+RlJ8NEYrER/R4OT3QjJFWBCGgAdt7uN1tWIIfpt 9Hs8EODmZ78q/EWuz3l93EyUyvIRehQ6d3h+0UAUz/2w/dQj5oC3X02XypniOZjYuq ffbkqnYHOVwEEbImelUYNI9sFJ9cGDOMJyD8wKV8= X-SMAIL-HELO: localhost.localdomain Received: from unknown (HELO localhost.localdomain)([114.249.62.144]) by sina.com (10.54.253.33) with ESMTP id 6A55BD5400007C9F; Tue, 14 Jul 2026 12:38:47 +0800 (CST) X-Sender: hdanton@sina.com X-Auth-ID: hdanton@sina.com Authentication-Results: sina.com; spf=none smtp.mailfrom=hdanton@sina.com; dkim=none header.i=none; dmarc=none action=none header.from=hdanton@sina.com X-SMAIL-MID: 3282726685363 X-SMAIL-UIID: 5C427D2DEC9C42C9A88BBEA97C916B4E-20260714-123847-1 From: Hillf Danton To: Tetsuo Handa Cc: Jens Axboe , Christoph Hellwig , linux-block , LKML , Linus Torvalds , linux-btrfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, Christian Brauner Subject: Re: [PATCH v4] loop: Fix NULL pointer dereference in lo_rw_aio() Date: Tue, 14 Jul 2026 12:38:33 +0800 Message-ID: <20260714043834.554-1-hdanton@sina.com> In-Reply-To: <33277fd6-0479-4f6c-bc21-f25f7179d2dc@I-love.SAKURA.ne.jp> References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit On Mon, 13 Jul 2026 20:02:52 +0900 Tetsuo Handa wrote: >On 2026/07/13 12:04, Hillf Danton wrote: >> On Tue, 9 Jun 2026 18:50:13 +0100 Al Viro wrote: >>> On Sun, Jun 07, 2026 at 07:54:58PM +0900, Tetsuo Handa wrote: >>>> syzbot is reporting NULL pointer dereference in lo_rw_aio() [1][2]. >>>> An analysis by the Gemini AI collaborator [3] considers that this problem >>>> is caused by a timing shift primarily exposed by commit 65565ca5f99b >>>> ("block: unify the synchronous bi_end_io callbacks"), along with helper >>>> refactorings like commit 92c3737a2473 ("block: add a bio_submit_or_kill >>>> helper"). >>>> >>>> But due to difficulty of reproducing this race, discussion about what is >>>> happening and how to fix this problem is stalling. Also, we haven't >>>> identified how many filesystems are subjected to this problem. >>>> >>>> Therefore, this patch introduces a grace period for flushing pending I/O >>>> requests (which should be a good thing from the perspective of defensive >>>> programming) so that we won't hit NULL pointer dereference problem, and >>>> also emits BUG: message in order to help filesystem developers identify >>>> the caller of an I/O request that failed to wait for completion so that >>>> filesystem developers can fix such caller to wait for completion. >>>> >>>> Note that emitting BUG: message is enabled only if CONFIG_KCOV=y, for >>>> this check is a waste of computation resources for almost all users. >>> >>> Still breaks xfs/259, same as the version in next-20260605... >>> >> And syzbot report [1] >> >> [1] https://lore.kernel.org/lkml/6a54399f.278cdcd2.e885.0023.GAE@google.com/ > > No. This report is from upstream tree where "loop: Fix NULL pointer dereference > in lo_rw_aio()" is not yet applied. > The issue remains but this work stalls.