Messages in this thread | | | Date | Tue, 7 Nov 2006 15:18:08 -0500 | From | "Mike Snitzer" <> | 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?
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