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Date:	Wed, 16 May 2012 22:55:05 +0800
From:	Tao Ma <tm@....ma>
To:	Eric Sandeen <sandeen@...hat.com>
CC:	linux-ext4@...r.kernel.org, Theodore Ts'o <tytso@....edu>
Subject: Re: [PATCH] ext4: Protect group inode free counting with group lock.

On 05/16/2012 09:43 PM, Eric Sandeen wrote:
> On 5/16/12 3:49 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:
> 
> This is only in the ! EXT4_FEATURE_RO_COMPAT_GDT_CSUM case I guess?
> That would be worth mentioning in the summary & changelog.
sure, I will add it in v2.
> 
> I guess you were testing without that for some reason?
See my comments below. I found it when running xfstests 269.

Thanks
Tao
> 
> -eric
> 
>> Free inodes count wrong for group #1 (1, counted=0).
>> Fix? no
>>
>> Free inodes count wrong for group #2 (3, counted=0).
>> Fix? no
>>
>> Directories count wrong for group #2 (780, counted=779).
>> Fix? no
>>
>> Free inodes count wrong for group #3 (2272, counted=2273).
>> Fix? no
>>
>> So this patch try to protect it with the ext4_lock_group.
>>
>> btw, it is found by xfstests test case 269 and I have run it 100
>> times and the error in e2fsck doesn't show up again.
>>
>> Cc: Theodore Ts'o <tytso@....edu>
>> Signed-off-by: Tao Ma <boyu.mt@...bao.com>
>> ---
>>  fs/ext4/ialloc.c |    9 +++++----
>>  1 files changed, 5 insertions(+), 4 deletions(-)
>>
>> 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);
>> +
>>  	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);
> 
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