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

[Eric Sandeen <sandeen sandeen net>]

Ingo Molnar wrote:
> * Srinivasa Ds <srinivasa 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