linux-ext4 - Re: [RFC][PATCH] Re: [BUG] ext4: cannot unfreeze a filesystem due to a deadlock

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Date:	Wed, 04 May 2011 09:30:27 -0500
From:	Eric Sandeen <sandeen@...hat.com>
To:	surbhi.palande@...ntu.com
CC:	Jan Kara <jack@...e.cz>, Dave Chinner <david@...morbit.com>,
	Toshiyuki Okajima <toshi.okajima@...fujitsu.com>,
	"Ted Ts'o" <tytso@....edu>,
	Masayoshi MIZUMA <m.mizuma@...fujitsu.com>,
	Andreas Dilger <adilger.kernel@...ger.ca>,
	linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	Christoph Hellwig <hch@...radead.org>
Subject: Re: [RFC][PATCH] Re: [BUG] ext4: cannot unfreeze a filesystem due
 to a deadlock

On 5/4/11 3:26 AM, Surbhi Palande wrote:
> On 05/03/2011 11:14 PM, Eric Sandeen wrote:
>> On 5/3/11 2:27 AM, Surbhi Palande wrote:

...

>>> Should this not be reverted? I think that its a lot easier to
>>> stop a transaction between a freeze and a thaw that way! If you
>>> agree, can I send a patch for the same?
>> Only if you want the kernel to start spewing "BUG!" messages
>> again...
>> 
>> -Eric
> But, then you need a much more complicated way to stop accepting the
> transactions and the writes between the freeze and the thaw? (in the
> write path and the read path)? Is this not much simpler?

I just cannot see how a solution which leads to:

>>      ================================================
>>      [ BUG: lock held when returning to user space! ]
>>      ------------------------------------------------
>>      lvcreate/1075 is leaving the kernel with locks still held!
>>      1 lock held by lvcreate/1075:
>>       #0:  (&journal->j_barrier){+.+...}, at: [<ffffffff811c6214>]
>>      jbd2_journal_lock_updates+0xe1/0xf0


can be considered viable.

You are welcome to send the patch, and if other ext4 devs concur with it then I'll be outvoted. :)

-Eric

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