From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-15.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY,URIBL_BLOCKED autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 76F98C433E2 for ; Tue, 1 Sep 2020 17:45:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 48C6E207D3 for ; Tue, 1 Sep 2020 17:45:58 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=oracle.com header.i=@oracle.com header.b="oazBklQ+" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726489AbgIARp5 (ORCPT ); Tue, 1 Sep 2020 13:45:57 -0400 Received: from aserp2120.oracle.com ([141.146.126.78]:48462 "EHLO aserp2120.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726139AbgIARpz (ORCPT ); Tue, 1 Sep 2020 13:45:55 -0400 Received: from pps.filterd (aserp2120.oracle.com [127.0.0.1]) by aserp2120.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 081HiDVO192493; Tue, 1 Sep 2020 17:45:42 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.com; h=date : from : to : cc : subject : message-id : references : mime-version : content-type : in-reply-to; s=corp-2020-01-29; bh=1kzS/sSaZV5K5kUKntVCCg//OiLp/QtmivDsc7LRoW4=; b=oazBklQ+ssS6xltqagzTnlUQrQIGZsImFZEUve8NcEo89gmVXOZmmfgp3rKuVX3pPPW7 kWNvKKVIXenUIEXLboW3CpVwuMsQzwbPvEbuRQTgDBtMBlkEhDjfTHG/PgG3XP/IOgWv CN13wuW71TRRQiFWW6PZ+MoIFrQCfTe+5+brtkcV8yukHnHLC3j5Uh9J0wbKzHW6NpQa Nxy+kvO/KYDI04XnAcfhKnoSJrA/opxHqMTCnhwesCdiKKDhGcry/gt9xGx2TanB1kBP 89FH1UbCx13Sax234FZmdx7TGLnj16C8DRPAVyxPJPXHc8W2w04yJhtrQ+wZdngIwX/A SQ== Received: from aserp3030.oracle.com (aserp3030.oracle.com [141.146.126.71]) by aserp2120.oracle.com with ESMTP id 337eym5we4-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL); Tue, 01 Sep 2020 17:45:42 +0000 Received: from pps.filterd (aserp3030.oracle.com [127.0.0.1]) by aserp3030.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 081HjCB3115625; Tue, 1 Sep 2020 17:45:42 GMT Received: from aserv0122.oracle.com (aserv0122.oracle.com [141.146.126.236]) by aserp3030.oracle.com with ESMTP id 3380knmgbx-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 01 Sep 2020 17:45:42 +0000 Received: from abhmp0016.oracle.com (abhmp0016.oracle.com [141.146.116.22]) by aserv0122.oracle.com (8.14.4/8.14.4) with ESMTP id 081HjeIu001367; Tue, 1 Sep 2020 17:45:40 GMT Received: from localhost (/10.159.133.7) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Tue, 01 Sep 2020 10:45:40 -0700 Date: Tue, 1 Sep 2020 10:45:38 -0700 From: "Darrick J. Wong" To: Josef Bacik Cc: Johannes Thumshirn , David Sterba , "linux-btrfs @ vger . kernel . org" , Filipe Manana , Christoph Hellwig , Linux FS Devel Subject: Re: [RFC PATCH] btrfs: don't call btrfs_sync_file from iomap context Message-ID: <20200901174538.GA6084@magnolia> References: <20200901130644.12655-1-johannes.thumshirn@wdc.com> <42efa646-73cd-d884-1c9c-dd889294bde2@toxicpanda.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <42efa646-73cd-d884-1c9c-dd889294bde2@toxicpanda.com> X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9731 signatures=668679 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 phishscore=0 spamscore=0 adultscore=0 mlxscore=0 suspectscore=0 malwarescore=0 mlxlogscore=999 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2006250000 definitions=main-2009010149 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9731 signatures=668679 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=0 adultscore=0 priorityscore=1501 phishscore=0 mlxlogscore=999 mlxscore=0 lowpriorityscore=0 clxscore=1011 spamscore=0 bulkscore=0 impostorscore=0 malwarescore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2006250000 definitions=main-2009010149 Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On Tue, Sep 01, 2020 at 11:11:58AM -0400, Josef Bacik wrote: > On 9/1/20 9:06 AM, Johannes Thumshirn wrote: > > Fstests generic/113 exposes a deadlock introduced by the switch to iomap > > for direct I/O. > > > > [ 18.291293] > > [ 18.291532] ============================================ > > [ 18.292115] WARNING: possible recursive locking detected > > [ 18.292723] 5.9.0-rc2+ #746 Not tainted > > [ 18.293145] -------------------------------------------- > > [ 18.293718] aio-stress/922 is trying to acquire lock: > > [ 18.294274] ffff888217412010 (&sb->s_type->i_mutex_key#11){++++}-{3:3}, at: btrfs_sync_file+0xf7/0x560 [btrfs] > > [ 18.295450] > > [ 18.295450] but task is already holding lock: > > [ 18.296086] ffff888217412010 (&sb->s_type->i_mutex_key#11){++++}-{3:3}, at: btrfs_file_write_iter+0x6e/0x630 [btrfs] > > [ 18.297249] > > [ 18.297249] other info that might help us debug this: > > [ 18.297960] Possible unsafe locking scenario: > > [ 18.297960] > > [ 18.298605] CPU0 > > [ 18.298880] ---- > > [ 18.299151] lock(&sb->s_type->i_mutex_key#11); > > [ 18.299653] lock(&sb->s_type->i_mutex_key#11); > > [ 18.300156] > > [ 18.300156] *** DEADLOCK *** > > [ 18.300156] > > [ 18.300802] May be due to missing lock nesting notation > > [ 18.300802] > > [ 18.301542] 2 locks held by aio-stress/922: > > [ 18.302000] #0: ffff888217412010 (&sb->s_type->i_mutex_key#11){++++}-{3:3}, at: btrfs_file_write_iter+0x6e/0x630 [btrfs] > > [ 18.303194] #1: ffff888217411ea0 (&ei->dio_sem){++++}-{3:3}, at: btrfs_direct_IO+0x113/0x160 [btrfs] > > [ 18.304223] > > [ 18.304223] stack backtrace: > > [ 18.304695] CPU: 0 PID: 922 Comm: aio-stress Not tainted 5.9.0-rc2+ #746 > > [ 18.305383] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.13.0-0-gf21b5a4-rebuilt.opensuse.org 04/01/2014 > > [ 18.306532] Call Trace: > > [ 18.306796] dump_stack+0x78/0xa0 > > [ 18.307145] __lock_acquire.cold+0x121/0x29f > > [ 18.307613] ? btrfs_dio_iomap_end+0x65/0x130 [btrfs] > > [ 18.308140] lock_acquire+0x93/0x3b0 > > [ 18.308544] ? btrfs_sync_file+0xf7/0x560 [btrfs] > > [ 18.309036] down_write+0x33/0x70 > > [ 18.309402] ? btrfs_sync_file+0xf7/0x560 [btrfs] > > [ 18.309912] btrfs_sync_file+0xf7/0x560 [btrfs] > > [ 18.310384] iomap_dio_complete+0x10d/0x120 > > [ 18.310824] iomap_dio_rw+0x3c8/0x520 > > [ 18.311225] btrfs_direct_IO+0xd3/0x160 [btrfs] > > [ 18.311727] btrfs_file_write_iter+0x1fe/0x630 [btrfs] > > [ 18.312264] ? find_held_lock+0x2b/0x80 > > [ 18.312662] aio_write+0xcd/0x180 > > [ 18.313011] ? __might_fault+0x31/0x80 > > [ 18.313408] ? find_held_lock+0x2b/0x80 > > [ 18.313817] ? __might_fault+0x31/0x80 > > [ 18.314217] io_submit_one+0x4e1/0xb30 > > [ 18.314606] ? find_held_lock+0x2b/0x80 > > [ 18.315010] __x64_sys_io_submit+0x71/0x220 > > [ 18.315449] do_syscall_64+0x33/0x40 > > [ 18.315829] entry_SYSCALL_64_after_hwframe+0x44/0xa9 > > [ 18.316363] RIP: 0033:0x7f5940881f79 > > [ 18.316740] Code: 00 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d e7 4e 0c 00 f7 d8 64 89 01 48 > > [ 18.318651] RSP: 002b:00007f5934f51d88 EFLAGS: 00000246 ORIG_RAX: 00000000000000d1 > > [ 18.319428] RAX: ffffffffffffffda RBX: 00007f5934f52680 RCX: 00007f5940881f79 > > [ 18.320168] RDX: 0000000000b56030 RSI: 0000000000000008 RDI: 00007f593171f000 > > [ 18.320895] RBP: 00007f593171f000 R08: 0000000000000000 R09: 0000000000b56030 > > [ 18.321630] R10: 00007fffd599e080 R11: 0000000000000246 R12: 0000000000000008 > > [ 18.322369] R13: 0000000000000000 R14: 0000000000b56030 R15: 0000000000b56070 > > > > This happens because iomap_dio_complete() calls into generic_write_sync() > > if we have the data-sync flag set. But as we're still under the > > inode_lock() from btrfs_file_write_iter() we will deadlock once > > btrfs_sync_file() tries to acquire the inode_lock(). > > > > Calling into generic_write_sync() is not needed as __btrfs_direct_write() > > already takes care of persisting the data on disk. We can temporarily drop > > the IOCB_DSYNC flag before calling into __btrfs_direct_write() so the > > iomap code won't try to call into the sync routines as well. > > > > References: https://github.com/btrfs/fstests/issues/12 > > Fixes: da4d7c1b4c45 ("btrfs: switch to iomap for direct IO") > > Signed-off-by: Johannes Thumshirn > > --- > > fs/btrfs/file.c | 5 ++++- > > 1 file changed, 4 insertions(+), 1 deletion(-) > > > > diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c > > index b62679382799..c75c0f2a5f72 100644 > > --- a/fs/btrfs/file.c > > +++ b/fs/btrfs/file.c > > @@ -2023,6 +2023,7 @@ static ssize_t btrfs_file_write_iter(struct kiocb *iocb, > > atomic_inc(&BTRFS_I(inode)->sync_writers); > > if (iocb->ki_flags & IOCB_DIRECT) { > > + iocb->ki_flags &= ~IOCB_DSYNC; > > num_written = __btrfs_direct_write(iocb, from); > > } else { > > num_written = btrfs_buffered_write(iocb, from); > > @@ -2046,8 +2047,10 @@ static ssize_t btrfs_file_write_iter(struct kiocb *iocb, > > if (num_written > 0) > > num_written = generic_write_sync(iocb, num_written); > > - if (sync) > > + if (sync) { > > + iocb->ki_flags |= IOCB_DSYNC; > > atomic_dec(&BTRFS_I(inode)->sync_writers); > > + } > > out: > > current->backing_dev_info = NULL; > > return num_written ? num_written : err; > > > > Christoph, I feel like this is broken. Xfs and ext4 get away with this for > different reasons, ext4 doesn't take the inode_lock() at all in fsync, and > xfs takes the ILOCK instead of the IOLOCK, so it's fine. However btrfs uses > inode_lock() in ->fsync (not for the IO, just for the logging part). A long > time ago I specifically pushed the inode locking down into ->fsync() > handlers to give us this sort of control. > > I'm not 100% on the iomap stuff, but the fix seems like we need to move the > generic_write_sync() out of iomap_dio_complete() completely, and the callers > do their own thing, much like the normal generic_file_write_iter() does. > And then I'd like to add a WARN_ON(lockdep_is_held()) in vfs_fsync_range() > so we can avoid this sort of thing in the future. What do you think? Hmm, I was under the impression that the direct write completion in either path (iomap or classic) could call generic_write_sync? How did this work in btrfs before the iomap conversion? --D > Thanks, > > Josef >