linux-kernel - Re: [RFC] Reverting "bd_mount_mutex" to "bd_mount

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Date:	Tue, 10 Oct 2006 20:34:30 +0530
From:	Srinivasa Ds <srinivasa@...ibm.com>
To:	Eric Sandeen <sandeen@...deen.net>
CC:	Ingo Molnar <mingo@...e.hu>, dm-devel@...hat.com,
	linux-lvm@...hat.com, linux-kernel@...r.kernel.org, agk@...hat.com
Subject: Re: [RFC] Reverting "bd_mount_mutex" to "bd_mount_sem"

Eric Sandeen wrote:
> Ingo Molnar wrote:
>   
>> * Srinivasa Ds <srinivasa@...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@...ibm.com>



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