From patchwork Mon Mar 9 18:57:14 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Eric Biggers X-Patchwork-Id: 11427785 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 831FE139A for ; Mon, 9 Mar 2020 18:58:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 63ED620873 for ; Mon, 9 Mar 2020 18:58:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1583780334; bh=B1UyNcxLW8PyJe3Q75G0rqEkEz05Wmj5+QamNjOuhpE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=Zz0v6VcMMTrEKCsosgy9o8ODaZvWTbHfaNY/82IW7g9DoZXvYxJZbvZJtG/g3YMsM qiMyCrJbDaydBFLeqi8Pysf8GxAQ9keMzCeuxtw4VKWmt+D924X8k8Q+2IYIVmUOTx 7510thO99ugLZKCDL5adcOOhH4qTTjDhOY/P7u6Q= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727451AbgCIS6v (ORCPT ); Mon, 9 Mar 2020 14:58:51 -0400 Received: from mail.kernel.org ([198.145.29.99]:46066 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727387AbgCIS6u (ORCPT ); Mon, 9 Mar 2020 14:58:50 -0400 Received: from sol.hsd1.ca.comcast.net (c-107-3-166-239.hsd1.ca.comcast.net [107.3.166.239]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id C906820866; Mon, 9 Mar 2020 18:58:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1583780330; bh=B1UyNcxLW8PyJe3Q75G0rqEkEz05Wmj5+QamNjOuhpE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=T7PsOBZw10bgq729PHYbEjWzwCGV7EzrsIszS8j0MmdQNps/ZBwz1vdlaqCCZT5TV kYdLL1f3WRO8gXYwXh2WInGSNQZKlkEw/OwvgL8V95Zex7gvHoHc+q1daW5TZ5fXwS nQgFwKiYLC9xg3s7LNqzl4cHDR7qK93ab5NWmqnQ= From: Eric Biggers To: linux-xfs@vger.kernel.org Cc: linux-ext4@vger.kernel.org, syzkaller-bugs@googlegroups.com, linux-kernel@vger.kernel.org Subject: [PATCH v3] xfs: clear PF_MEMALLOC before exiting xfsaild thread Date: Mon, 9 Mar 2020 11:57:14 -0700 Message-Id: <20200309185714.42850-1-ebiggers@kernel.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20200309181332.GJ1752567@magnolia> References: <20200309181332.GJ1752567@magnolia> MIME-Version: 1.0 Sender: linux-xfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org From: Eric Biggers Leaving PF_MEMALLOC set when exiting a kthread causes it to remain set during do_exit(). That can confuse things. In particular, if BSD process accounting is enabled, then do_exit() writes data to an accounting file. If that file has FS_SYNC_FL set, then this write occurs synchronously and can misbehave if PF_MEMALLOC is set. For example, if the accounting file is located on an XFS filesystem, then a WARN_ON_ONCE() in iomap_do_writepage() is triggered and the data doesn't get written when it should. Or if the accounting file is located on an ext4 filesystem without a journal, then a WARN_ON_ONCE() in ext4_write_inode() is triggered and the inode doesn't get written. Fix this in xfsaild() by using the helper functions to save and restore PF_MEMALLOC. This can be reproduced as follows in the kvm-xfstests test appliance modified to add the 'acct' Debian package, and with kvm-xfstests's recommended kconfig modified to add CONFIG_BSD_PROCESS_ACCT=y: mkfs.xfs -f /dev/vdb mount /vdb touch /vdb/file chattr +S /vdb/file accton /vdb/file mkfs.xfs -f /dev/vdc mount /vdc umount /vdc It causes: WARNING: CPU: 1 PID: 336 at fs/iomap/buffered-io.c:1534 CPU: 1 PID: 336 Comm: xfsaild/vdc Not tainted 5.6.0-rc5 #3 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS ?-20191223_100556-anatol 04/01/2014 RIP: 0010:iomap_do_writepage+0x16b/0x1f0 fs/iomap/buffered-io.c:1534 [...] Call Trace: write_cache_pages+0x189/0x4d0 mm/page-writeback.c:2238 iomap_writepages+0x1c/0x33 fs/iomap/buffered-io.c:1642 xfs_vm_writepages+0x65/0x90 fs/xfs/xfs_aops.c:578 do_writepages+0x41/0xe0 mm/page-writeback.c:2344 __filemap_fdatawrite_range+0xd2/0x120 mm/filemap.c:421 file_write_and_wait_range+0x71/0xc0 mm/filemap.c:760 xfs_file_fsync+0x7a/0x2b0 fs/xfs/xfs_file.c:114 generic_write_sync include/linux/fs.h:2867 [inline] xfs_file_buffered_aio_write+0x379/0x3b0 fs/xfs/xfs_file.c:691 call_write_iter include/linux/fs.h:1901 [inline] new_sync_write+0x130/0x1d0 fs/read_write.c:483 __kernel_write+0x54/0xe0 fs/read_write.c:515 do_acct_process+0x122/0x170 kernel/acct.c:522 slow_acct_process kernel/acct.c:581 [inline] acct_process+0x1d4/0x27c kernel/acct.c:607 do_exit+0x83d/0xbc0 kernel/exit.c:791 kthread+0xf1/0x140 kernel/kthread.c:257 ret_from_fork+0x27/0x50 arch/x86/entry/entry_64.S:352 This bug was originally reported by syzbot at https://lore.kernel.org/r/0000000000000e7156059f751d7b@google.com. Reported-by: syzbot+1f9dc49e8de2582d90c2@syzkaller.appspotmail.com Signed-off-by: Eric Biggers Reviewed-by: Darrick J. Wong Reviewed-by: Christoph Hellwig --- v3: updated commit message again, this time to take into account the bug also being reproducible when the accounting file is located on XFS. v2: include more details in the commit message. fs/xfs/xfs_trans_ail.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/fs/xfs/xfs_trans_ail.c b/fs/xfs/xfs_trans_ail.c index 00cc5b8734be8..3bc570c90ad97 100644 --- a/fs/xfs/xfs_trans_ail.c +++ b/fs/xfs/xfs_trans_ail.c @@ -529,8 +529,9 @@ xfsaild( { struct xfs_ail *ailp = data; long tout = 0; /* milliseconds */ + unsigned int noreclaim_flag; - current->flags |= PF_MEMALLOC; + noreclaim_flag = memalloc_noreclaim_save(); set_freezable(); while (1) { @@ -601,6 +602,7 @@ xfsaild( tout = xfsaild_push(ailp); } + memalloc_noreclaim_restore(noreclaim_flag); return 0; }