[linux-lvm] Re: [RFC] Reverting "bd_mount_mutex" to "bd_mount_sem"

Srinivasa Ds srinivasa at in.ibm.com
Tue Oct 10 15:04:30 UTC 2006

Eric Sandeen wrote:
> Ingo Molnar wrote:
>> * Srinivasa Ds <srinivasa at in.ibm.com> wrote:
>>>   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.
>> hm, to me this seems quite a fragile construct - even if the 
>> mutex-debugging warning is worked around by reverting to a semaphore.
>> 	Ingo
> Ingo, what do you feel is fragile about this?  It seems like this is a
> reasonable way to go, except that maybe a down_trylock would be good if
> a 2nd process tries to freeze while it's already frozen...
> Thanks,
> -Eric
Ingo, As per the discussion resending the patch with down_trylock.

Signed-off-by: Srinivasa DS <srinivasa at in.ibm.com>

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