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

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Message-ID: <4526C184.7070507@sandeen.net>
Date:	Fri, 06 Oct 2006 15:50:12 -0500
From:	Eric Sandeen <sandeen@...deen.net>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Srinivasa Ds <srinivasa@...ibm.com>, 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"

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
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