From: "Takashi Sato" <t-sato@yk.jp.nec.com>
Subject: Re: [RFC PATCH 1/3] Implement generic freeze feature
Date: Wed, 30 Apr 2008 10:10:13 +0900
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To: "Christoph Hellwig" <hch@infradead.org>
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Hi,

>> 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.

I think the bit flag is more efficient than the semaphore.
So I will consider whether it can be used for the freeze feature.

Cheers, Takashi