From: Christoph Hellwig <hch@lst.de>
To: Jan Kara <jack@suse.cz>
Cc: Dmitry Monakhov <dmonakhov@openvz.org>,
Camille Moncelier <pix@devlife.org>,
"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
ext4 development <linux-ext4@vger.kernel.org>,
hch@lst.de, viro@zeniv.linux.org.uk
Subject: Re: [ext3] Changes to block device after an ext3 mount point has been remounted readonly
Date: Tue, 2 Mar 2010 10:34:31 +0100 [thread overview]
Message-ID: <20100302093431.GB5106@lst.de> (raw)
In-Reply-To: <20100224165646.GL3687@quack.suse.cz>
On Wed, Feb 24, 2010 at 05:56:46PM +0100, Jan Kara wrote:
> OK, I see that in theory a process can open file for writing after
> fs_may_remount_ro() before MS_RDONLY flag gets set. That could be really
> nasty.
Not just in theory, but also in practice. We can easily hit this under
load with XFS.
> But by no means we should solve this VFS problem by spilling error
> messages from the filesystem.
Exactly.
> Al, Christoph, do I miss something or there is really nothing which
> prevents a process from opening a file after the fs_may_remount_ro() check
> in do_remount_sb()?
No, there is nothing. We really do need a multi-stage remount read-only
process:
1) stop any writes from userland, that is opening new files writeable
2) stop any periodic writeback from the VM or filesystem-internal
3) write out all filesystem data and metadata
4) mark the filesystem fully read-only
next prev parent reply other threads:[~2010-03-02 9:34 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-02-18 16:45 [ext3] Changes to block device after an ext3 mount point has been remounted readonly PiX
2010-02-18 16:50 ` Camille Moncelier
2010-02-18 21:41 ` Andreas Dilger
2010-02-19 7:38 ` Camille Moncelier
2010-02-22 22:32 ` Jan Kara
2010-02-22 23:05 ` Jan Kara
2010-02-22 23:09 ` Andreas Dilger
2010-02-23 8:42 ` Camille Moncelier
2010-02-23 13:55 ` Jan Kara
2010-02-24 16:01 ` Dmitry Monakhov
2010-02-24 16:26 ` Camille Moncelier
2010-02-24 16:59 ` Jan Kara
2010-02-24 16:56 ` Jan Kara
2010-03-02 9:34 ` Christoph Hellwig [this message]
2010-03-02 10:01 ` Dmitry Monakhov
2010-03-02 13:26 ` Jan Kara
2010-03-02 23:10 ` Joel Becker
2010-02-24 16:57 ` Eric Sandeen
2010-02-24 17:05 ` Jan Kara
2010-02-24 17:26 ` Dmitry Monakhov
2010-02-24 21:36 ` Jan Kara
2010-03-02 10:29 ` Nick Piggin
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