Re: [PATCH 7/9] vfs: protect remounting superblock read-only

From: Al Viro
Date: Fri Oct 22 2010 - 02:46:45 EST


On Tue, Oct 05, 2010 at 12:31:15PM +0200, Miklos Szeredi wrote:
> From: Miklos Szeredi <mszeredi@xxxxxxx>
>
> 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.
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