linux-ext4 - Re: [PATCH] ext4: fix unhandled ext4_free

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Date:	Sun, 11 Jan 2009 08:46:32 -0600
From:	Eric Sandeen <sandeen@...hat.com>
To:	Josef Bacik <jbacik@...hat.com>
CC:	Akinobu Mita <akinobu.mita@...il.com>,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	Theodore Tso <tytso@....edu>, adilger@....com,
	linux-ext4@...r.kernel.org
Subject: Re: [PATCH] ext4: fix unhandled ext4_free_data allocation failure

Josef Bacik wrote:
> On Sun, Jan 11, 2009 at 11:03:53AM +0900, Akinobu Mita wrote:
>> In ext4_mb_free_blocks() ext4_free_data allocation failure
>> is not handled. This error handling cannot be simple error return because
>> ext4_mb_free_blocks() cannot fail.
>>
>> This patch add __GFP_NOFAIL to gfp mask for the allocation.
>>
>> Cc: Theodore Tso <tytso@....edu>
>> Cc: adilger@....com
>> Cc: linux-ext4@...r.kernel.org
>> Signed-off-by: Akinobu Mita <akinobu.mita@...il.com>
> 
> Sorry but thats still not right, the fs should never force the box to come up
> with memory, it should be able to gracefully handle ENOMEM cases.  This patch
> does this properly.  Thanks,
> 
> Signed-off-by: Josef Bacik <jbacik@...hat.com>
> 
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index 918aec0..e97ea09 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -4886,6 +4886,10 @@ do_more:
>  		 * be used until this transaction is committed
>  		 */
>  		new_entry  = kmem_cache_alloc(ext4_free_ext_cachep, GFP_NOFS);
> +		if (!new_entry) {
> +			err = -ENOMEM;
> +			goto error_return;
> +		}
>  		new_entry->start_blk = bit;
>  		new_entry->group  = block_group;
>  		new_entry->count = count;

Well, this will now force a filesystem error (then remount-ro or panic
(or ignore) if the allocation fails.  I'm not sure that's better...?

-Eric
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