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Message-ID: <170fa0d20611071218t3c145ef9i5413e432597d78a5@mail.gmail.com> Date: Tue, 7 Nov 2006 15:18:08 -0500 From: "Mike Snitzer" <snitzer@...il.com> To: "device-mapper development" <dm-devel@...hat.com>, "Andrew Morton" <akpm@...l.org>, linux-kernel@...r.kernel.org, "Ingo Molnar" <mingo@...e.hu>, "Eric Sandeen" <sandeen@...deen.net>, "Srinivasa DS" <srinivasa@...ibm.com> Subject: Re: [dm-devel] [PATCH 2.6.19 5/5] fs: freeze_bdev with semaphore not mutex On 11/7/06, Alasdair G Kergon <agk@...hat.com> wrote: > From: Srinivasa Ds <srinivasa@...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 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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