linux-ext4 - Re: [PATCH v2] Adding support to freeze and unfreeze a journal

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Message-ID: <4DC7F0E4.5070507@canonical.com>
Date:	Mon, 09 May 2011 16:49:24 +0300
From:	Surbhi Palande <surbhi.palande@...onical.com>
To:	Jan Kara <jack@...e.cz>
CC:	adilger.kernel@...ger.ca, toshi.okajima@...fujitsu.com,
	marco.stornelli@...il.com, tytso@....edu, m.mizuma@...fujitsu.com,
	linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	sandeen@...hat.com
Subject: Re: [PATCH v2] Adding support to freeze and unfreeze a journal

On 05/09/2011 12:53 PM, Jan Kara wrote:
> On Sat 07-05-11 23:04:22, Surbhi Palande wrote:
>> +void jbd2_journal_thaw(journal_t * journal)
>> +{
>> +	write_lock(&journal->j_state_lock);
>> +	journal->j_flags = journal->j_flags&= ~JBD2_FROZEN;
>> +	write_unlock(&journal->j_state_lock);
>> +	smp_wmb();
>    Why is here the smp_wmb()? The write is inside a rw-lock so it cannot be
> reordered. Also wake_up() is protected by queue->lock so I don't see the
> need for a barrier.

Ok, thanks for letting me know. I was under the impression that a 
reorder was possible in case of SMP. I will rewrite the patch with this 
change and the one that Marco Stornelli suggested as well.

Thanks a lot!

Warm Regards,
Surbhi.

>
>> +	wake_up(&journal->j_wait_frozen);
>> +}
>> +EXPORT_SYMBOL(jbd2_journal_thaw);
>
> 								Honza

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