linux-kernel - Re: [RFC PATCH 1/3] Implement generic freeze feature

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Message-ID: <20080428130358.GB2798@infradead.org>
Date:	Mon, 28 Apr 2008 09:03:58 -0400
From:	Christoph Hellwig <hch@...radead.org>
To:	Takashi Sato <t-sato@...jp.nec.com>
Cc:	Christoph Hellwig <hch@...radead.org>, linux-ext4@...r.kernel.org,
	xfs@....sgi.com, dm-devel@...hat.com,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 1/3] Implement generic freeze feature

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.

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