linux-kernel - Re: [RFC][PATCH] fs: Prevent syncing frozen file system

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Message-ID: <20150710004921.GJ3902@dastard>
Date:	Fri, 10 Jul 2015 10:49:21 +1000
From:	Dave Chinner <david@...morbit.com>
To:	Lukas Czerner <lczerner@...hat.com>
Cc:	viro@...IV.linux.org.uk, bfields@...ldses.org,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [RFC][PATCH] fs: Prevent syncing frozen file system

On Fri, Jul 10, 2015 at 09:40:12AM +1000, Dave Chinner wrote:
> On Thu, Jul 09, 2015 at 07:45:45PM +0200, Lukas Czerner wrote:
> > Currently we can end up in a deadlock because of broken
> > sb_start_write -> s_umount ordering.
> > 
> > The race goes like this:
> > 
> >  - write the file
> >  - unlink the file - final_iput will not be calles as file is opened
> >  - freeze the file system
> >  - Now simultaneously close the file and call sync (or syncfs on that
> >    particular file system). Sync will get to wait_sb_inodes() where it will
> >    grab the referece to the inode (__iget()) and later to call iput().
> 
> This problem goes away with the sync scalability patchset that josef
> has been trying to get merged:
> 
> git://git.kernel.org/pub/scm/linux/kernel/git/josef/btrfs-next.git superblock-scaling
> 
> That patchset removes the full sb inodes list walk in
> wait_sb_inodes() and replaces it with a walk of inodes cleaned
> during the sync, which will be an empty list in the case of sync
> running on an empty filesystem. This commit does the work:

s/empty/frozen

-Dave.
-- 
Dave Chinner
david@...morbit.com
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