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Date: Fri, 22 Oct 2010 07:46:27 +0100
From: Al Viro <viro@ZenIV.linux.org.uk>
To: Miklos Szeredi <miklos@szeredi.hu>
Cc: dave@linux.vnet.ibm.com, akpm@linux-foundation.org,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 7/9] vfs: protect remounting superblock read-only
Message-ID: <20101022064627.GA21607@ZenIV.linux.org.uk>
References: <20101005103108.288743609@szeredi.hu>
 <20101005103144.051231469@szeredi.hu>
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On Tue, Oct 05, 2010 at 12:31:15PM +0200, Miklos Szeredi wrote:
> From: Miklos Szeredi <mszeredi@suse.cz>
> 
> Currently remouting superblock read-only is racy in a major way.
> 
> With the per mount read-only infrastructure it is now possible to
> prevent most races, which this patch attempts.
> 
> Before starting the remount read-only, set MNT_WRITE_HOLD on all
> mounts so that writes are held off until the remount either succeeds
> or fails.

Umm...  What'll happen if your remount will say mnt_want_write() on
e.g. internal vfsmount over that sb?  Or, more subtle, tries to
update atime on some opened struct file on that sb.