From: Chandan Rajendra <chandan@linux.vnet.ibm.com>
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 15:57:40 +0530 [thread overview]
Message-ID: <25132456.GqS7QuRSzf@localhost.localdomain> (raw)
In-Reply-To: <1482485418-4190-1-git-send-email-chandan@linux.vnet.ibm.com>
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.
--
chandan
next prev parent reply other threads:[~2016-12-23 10:27 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-12-23 9:30 [PATCH] Btrfs: Fix deadlock between direct IO and fast fsync Chandan Rajendra
2016-12-23 10:27 ` Chandan Rajendra [this message]
2016-12-23 11:57 ` Chandan Rajendra
2016-12-24 0:18 ` Liu Bo
2016-12-24 3:27 ` Chandan Rajendra
2017-01-02 14:29 ` David Sterba
2017-01-06 11:45 ` Filipe Manana
2017-01-06 12:18 ` David Sterba
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=25132456.GqS7QuRSzf@localhost.localdomain \
--to=chandan@linux.vnet.ibm.com \
--cc=dsterba@suse.com \
--cc=fdmanana@suse.com \
--cc=linux-btrfs@vger.kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).