linux-ext4 - Re: potential memory leak on transaction commit

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Date:	Tue, 8 Mar 2011 14:16:29 +0100 (CET)
From:	Lukas Czerner <lczerner@...hat.com>
To:	Zhang Huan <zhhuan@...il.com>
cc:	linux-ext4@...r.kernel.org
Subject: Re: potential memory leak on transaction commit

On Tue, 8 Mar 2011, Zhang Huan wrote:

> Hi all,
> 
> There is potential memory leak of journal head in function
> jbd2_journal_commit_transaction. The problem is that JBD2 will not
> reclaim the journal head of commit record if error occurs or journal is
> abotred.
> 
> I use the following script to reproduce this issue, on a RHEL6 system. I
> found it very easy to reproduce with async commit enabled.
> 
> mount /dev/sdb /mnt -o journal_checksum,journal_async_commit
> touch /mnt/xxx
> echo offline > /sys/block/sdb/device/state
> sync
> umount /mnt
> rmmod ext4
> rmmod jbd2
> 
> Removal of the jbd2 module will make slab complaining that
> "cache `jbd2_journal_head': can't free all objects".
> 
> 
> Here is my fix for this issue. The commit record should be reclaimed no
> matter error occurs or not.
> 
> diff --git a/fs/jbd2/commit.c b/fs/jbd2/commit.c
> index f3ad159..37a973a 100644
> --- a/fs/jbd2/commit.c
> +++ b/fs/jbd2/commit.c
> @@ -105,6 +105,8 @@ static int journal_submit_commit_record(journal_t *journal,
>  	int ret;
>  	struct timespec now = current_kernel_time();
>  
> +	*cbh = NULL;
> +
>  	if (is_journal_aborted(journal))
>  		return 0;
>  
> @@ -808,7 +810,7 @@ wait_for_iobuf:
>  		if (err)
>  			__jbd2_journal_abort_hard(journal);
>  	}
> -	if (!err && !is_journal_aborted(journal))
> +	if (cbh)

Hi,

I wonder if we could do rather this:

	if (!err && !is_journal_aborted(journal))
		err = journal_wait_on_commit_record(journal, cbh);
	else if (cbh) {
		put_bh(cbh);
		jbd2_journal_put_journal_head(bh2jh(cbh));
	}

I think this is more readable...

Thanks!
-Lukas

>  		err = journal_wait_on_commit_record(journal, cbh);
>  	if (JBD2_HAS_INCOMPAT_FEATURE(journal,
>  				      JBD2_FEATURE_INCOMPAT_ASYNC_COMMIT) &&
> 
> 
> 
> PS: Just out of curiosity, why would journal_submit_commit_record return a
> value of 1 instead of an error number if get descriptor buffer is failed.
> 
> 
> Zhang Huan
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