From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:42592 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751500AbcLWL6O (ORCPT ); Fri, 23 Dec 2016 06:58:14 -0500 Received: from pps.filterd (m0098399.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.17/8.16.0.17) with SMTP id uBNBrtR8106769 for ; Fri, 23 Dec 2016 06:58:13 -0500 Received: from e28smtp01.in.ibm.com (e28smtp01.in.ibm.com [125.16.236.1]) by mx0a-001b2d01.pphosted.com with ESMTP id 27guk8fkv0-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Fri, 23 Dec 2016 06:58:13 -0500 Received: from localhost by e28smtp01.in.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Fri, 23 Dec 2016 17:28:09 +0530 Received: from d28relay04.in.ibm.com (d28relay04.in.ibm.com [9.184.220.61]) by d28dlp02.in.ibm.com (Postfix) with ESMTP id D79FB394005C for ; Fri, 23 Dec 2016 17:28:06 +0530 (IST) Received: from d28av07.in.ibm.com (d28av07.in.ibm.com [9.184.220.146]) by d28relay04.in.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id uBNBvxkv27984012 for ; Fri, 23 Dec 2016 17:28:00 +0530 Received: from d28av07.in.ibm.com (localhost [127.0.0.1]) by d28av07.in.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id uBNBvw1L022976 for ; Fri, 23 Dec 2016 17:27:58 +0530 From: Chandan Rajendra To: linux-btrfs@vger.kernel.org Cc: fdmanana@suse.com, dsterba@suse.com Subject: Re: [PATCH] Btrfs: Fix deadlock between direct IO and fast fsync Date: Fri, 23 Dec 2016 17:27:55 +0530 In-Reply-To: <25132456.GqS7QuRSzf@localhost.localdomain> References: <1482485418-4190-1-git-send-email-chandan@linux.vnet.ibm.com> <25132456.GqS7QuRSzf@localhost.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Message-Id: <2606394.PBVynvYKAF@localhost.localdomain> Sender: linux-btrfs-owner@vger.kernel.org List-ID: On Friday, December 23, 2016 03:57:40 PM Chandan Rajendra wrote: > On Friday, December 23, 2016 03:00:18 PM Chandan Rajendra wrote: > > The following deadlock is seen when executing generic/113 test, > > > > ---------------------------------------------------------+---------------------------------------------------- > > Direct I/O task Fast fsync task > > ---------------------------------------------------------+---------------------------------------------------- > > btrfs_direct_IO > > __blockdev_direct_IO > > do_blockdev_direct_IO > > do_direct_IO > > btrfs_get_blocks_direct > > while (blocks needs to written) > > get_more_blocks (first iteration) > > btrfs_get_blocks_direct > > btrfs_create_dio_extent > > down_read(&BTRFS_I(inode) >dio_sem) > > Create and add extent map and ordered extent > > up_read(&BTRFS_I(inode) >dio_sem) > > btrfs_sync_file > > btrfs_log_dentry_safe > > btrfs_log_inode_parent > > btrfs_log_inode > > btrfs_log_changed_extents > > down_write(&BTRFS_I(inode) >dio_sem) > > Collect new extent maps and ordered extents > > wait for ordered extent completion > > get_more_blocks (second iteration) > > btrfs_get_blocks_direct > > btrfs_create_dio_extent > > down_read(&BTRFS_I(inode) >dio_sem) > > -------------------------------------------------------------------------------------------------------------- > > > > In the above description, Btrfs direct I/O code path has not yet started > > submitting bios for file range covered by the initial ordered > > extent. Meanwhile, The fast fsync task obtains the write semaphore and > > waits for I/O on the ordered extent to get completed. However, the > > Direct I/O task is now blocked on obtaining the read semaphore. > > > > To resolve the deadlock, this commit modifies the Direct I/O code path > > to obtain the read semaphore before invoking > > __blockdev_direct_IO(). The semaphore is then given up after > > __blockdev_direct_IO() returns. This allows the Direct I/O code to > > complete I/O on all the ordered extents it creates. > > > > Btw, I was able to reproduce the issue on kdave/for-next branch with "Merge > branch 'for-next-next-4.9-20161125' into for-next-20161125" as the topmost > commit. The issue cannot be reproduced yet on latest code available from > kdave/for-next branch. > > Maybe changes in upstream might have masked the issue in the recent kdave/for-next branch. I say that because 'git bisect' resulted in the following commit ... e3597e6090ddf40904dce6d0a5a404e2c490cac6 Author: Chris Mason AuthorDate: Tue Nov 1 12:54:45 2016 -0700 Commit: Chris Mason CommitDate: Tue Nov 1 12:54:45 2016 -0700 Parent: 570dd45 btrfs: fix races on root_log_ctx lists Parent: 9d1032c btrfs: fix WARNING in btrfs_select_ref_head() Merged: btrfs-next-for-linus-4.8 kdave-master linus-v4.7-rc6 local-v4.7-rc4 Containing: direct-io-fsync-deadlock kdave-for-next Follows: v4.8-rc8 (57) Precedes: next-20161219 (30006) Merge branch 'for-4.9-rc3' of git://git.kernel.org/pub/scm/linux/kernel/git/kdave/linux into for-linus-4.9 5 files changed, 29 insertions(+), 9 deletions(-) fs/btrfs/extent-tree.c | 3 +++ fs/btrfs/extent_io.c | 8 ++++---- fs/btrfs/inode.c | 13 +++++++++---- fs/btrfs/ioctl.c | 5 +++++ fs/btrfs/relocation.c | 9 ++++++++- -- chandan