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

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Message-Id: <D8E7FEBEEB9649CF9E2FC389BC5F8C6B@nsl.ad.nec.co.jp>
Date:	Wed, 30 Apr 2008 10:10:13 +0900
From:	"Takashi Sato" <t-sato@...jp.nec.com>
To:	"Christoph Hellwig" <hch@...radead.org>
Cc:	<linux-kernel@...r.kernel.org>, <linux-fsdevel@...r.kernel.org>,
	<dm-devel@...hat.com>, <xfs@....sgi.com>,
	<linux-ext4@...r.kernel.org>
Subject: Re: [RFC PATCH 1/3] Implement generic freeze feature

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
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