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Message-ID: <170fa0d20611071218t3c145ef9i5413e432597d78a5@mail.gmail.com>
Date: Tue, 7 Nov 2006 15:18:08 -0500
From: "Mike Snitzer" <snitzer@gmail.com>
To: "device-mapper development" <dm-devel@redhat.com>,
       "Andrew Morton" <akpm@osdl.org>, linux-kernel@vger.kernel.org,
       "Ingo Molnar" <mingo@elte.hu>, "Eric Sandeen" <sandeen@sandeen.net>,
       "Srinivasa DS" <srinivasa@in.ibm.com>
Subject: Re: [dm-devel] [PATCH 2.6.19 5/5] fs: freeze_bdev with semaphore not mutex
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On 11/7/06, Alasdair G Kergon <agk@redhat.com> wrote:
> From: Srinivasa Ds <srinivasa@in.ibm.com>
>
> On debugging I found out that,"dmsetup suspend <device name>" calls
> "freeze_bdev()",which locks "bd_mount_mutex" to make sure that no new mounts
> happen on bdev until thaw_bdev() is called.  This "thaw_bdev()" is getting
> called when we resume the device through "dmsetup resume <device-name>".
> Hence we have 2 processes,one of which locks "bd_mount_mutex"(dmsetup
> suspend) and another(dmsetup resume) unlocks it.

Srinivasa's description of the patch just speaks to how freeze_bdev
and thaw_bdev are used by DM but completely skips justification for
switching from mutex to semaphore.  Why is it beneficial and/or
necessary to use a semaphore instead of a mutex here?

Mike
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