Messages in this thread Patch in this message | | | Date | Tue, 7 Nov 2006 12:28:37 -0800 | From | Andrew Morton <> | Subject | Re: [PATCH 2.6.19 5/5] fs: freeze_bdev with semaphore not mutex |
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On Tue, 7 Nov 2006 18:34:59 +0000 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.
So... what does this have to do with switching from mutex to semaphore?
Perhaps this works around the debugging code which gets offended if a mutex is unlocked by a process which didn't do the lock?
If so, it's a bit sad to switch to semaphore just because of some errant debugging code. Perhaps it would be better to create a new mutex_unlock_stfu() which suppresses the warning?
> --- linux-2.6.19-rc4.orig/fs/buffer.c 2006-11-07 17:06:20.000000000 +0000 > +++ linux-2.6.19-rc4/fs/buffer.c 2006-11-07 17:26:04.000000000 +0000 > @@ -188,7 +188,9 @@ struct super_block *freeze_bdev(struct b > { > struct super_block *sb; > > - mutex_lock(&bdev->bd_mount_mutex); > + if (down_trylock(&bdev->bd_mount_sem)) > + return -EBUSY; > +
This is a functional change which isn't described in the changelog. What's happening here?
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