linux-ext4 - Re: [PATCH] ext4: Protect group inode free counting with group lock.

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Date:	Wed, 16 May 2012 08:58:23 -0600
From:	Andreas Dilger <adilger@...ger.ca>
To:	Tao Ma <tm@....ma>
Cc:	linux-ext4@...r.kernel.org, Theodore Ts'o <tytso@....edu>
Subject: Re: [PATCH] ext4: Protect group inode free counting with group lock.

On 2012-05-16, at 2:49 AM, Tao Ma wrote:
> From: Tao Ma <boyu.mt@...bao.com>
> 
> Now when we set the group inode free count, we don't have a proper
> group lock so that multiple threads may decrease the inode free
> count at the same time. And e2fsck will complain something like:
> 
> diff --git a/fs/ext4/ialloc.c b/fs/ext4/ialloc.c
> index 409c2ee..25595e2 100644
> --- a/fs/ext4/ialloc.c
> +++ b/fs/ext4/ialloc.c
> @@ -772,7 +772,9 @@ got:
> 			ext4_itable_unused_set(sb, gdp,
> 					(EXT4_INODES_PER_GROUP(sb) - ino));
> 		up_read(&grp->alloc_sem);
> -	}
> +	} else
> +		ext4_lock_group(sb, group);

Minor coding style fix - when one half of if/else is using braces
then the other half should also use braces, like:

	if {
		:
	} else {
		:
	}

> +
> 	ext4_free_inodes_set(sb, gdp, ext4_free_inodes_count(sb, gdp) - 1);
> 	if (S_ISDIR(mode)) {
> 		ext4_used_dirs_set(sb, gdp, ext4_used_dirs_count(sb, gdp) + 1);
> @@ -782,10 +784,9 @@ got:
> 			atomic_inc(&sbi->s_flex_groups[f].used_dirs);
> 		}
> 	}
> -	if (EXT4_HAS_RO_COMPAT_FEATURE(sb, EXT4_FEATURE_RO_COMPAT_GDT_CSUM)) {
> +	if (EXT4_HAS_RO_COMPAT_FEATURE(sb, EXT4_FEATURE_RO_COMPAT_GDT_CSUM))
> 		gdp->bg_checksum = ext4_group_desc_csum(sbi, group, gdp);
> -		ext4_unlock_group(sb, group);
> -	}
> +	ext4_unlock_group(sb, group);
> 
> 	BUFFER_TRACE(inode_bitmap_bh, "call ext4_handle_dirty_metadata");
> 	err = ext4_handle_dirty_metadata(handle, NULL, inode_bitmap_bh);
> -- 
> 1.7.1
> 
> --
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Cheers, Andreas





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