linux-ext4 - Re: [PATCH] ext4: fix error processing in mb_free

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Message-Id: <20080528213023.a703d10c.akpm@linux-foundation.org>
Date:	Wed, 28 May 2008 21:30:23 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Shen Feng <shen@...fujitsu.com>
Cc:	linux-ext4@...r.kernel.org, cmm@...ibm.com,
	aneesh.kumar@...ux.vnet.ibm.com
Subject: Re: [PATCH] ext4: fix error processing in mb_free_blocks

On Thu, 29 May 2008 11:21:18 +0800 Shen Feng <shen@...fujitsu.com> wrote:

> The error processing of the return value of mb_free_blocks
> is meanless because it only return 0. This fix includes
> *make mb_free_blocks return void
> *remove the error processing part in callers

This:

> *unlock group before calling ext4_error in mb_free_blocks

fixes a potential deadlock.

> @@ -1084,11 +1084,12 @@ static int mb_free_blocks(struct inode *inode, struct ext4_buddy *e4b,
>  			blocknr += block;
>  			blocknr +=
>  			    le32_to_cpu(EXT4_SB(sb)->s_es->s_first_data_block);
> -
> +			ext4_unlock_group(sb, e4b->bd_group);
>  			ext4_error(sb, __func__, "double-free of inode"
>  				   " %lu's block %llu(bit %u in group %lu)\n",
>  				   inode ? inode->i_ino : 0, blocknr, block,
>  				   e4b->bd_group);
> +			ext4_lock_group(sb, e4b->bd_group);
>  		}
>  		mb_clear_bit(block, EXT4_MB_BITMAP(e4b));
>  		e4b->bd_info->bb_counters[order]++;

but are we sure we can just drop the lock and then cheerfully proceed? 
Whatever data that lock is protecting might have changed..

A safer-looking fix would be to return an error from mb_free_blocks()
and handle the in the caller, once the ext4_unlock_group() has been
performed.

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