[dm-devel] Re: [RFC PATCH 1/3] Implement generic freeze feature

[Christoph Hellwig]

On Mon, Apr 28, 2008 at 09:59:55PM +0900, Takashi Sato wrote:
>> I think the protection against double freezes would be better done by
>> using a trylock on bd_mount_sem.
>
> bd_mount_sem can protect against only freezes and cannot protect against
> unfreezes.  If multiple unfreezes run in parallel,  the multiple up() for
> bd_mount_sem might occur incorrectly.

Indeed.  The bit flag would fix that because unfreeze could then check
for the bit beeing set first.  So that's probably the easiest way to go.