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List:       linux-btrfs
Subject:    Re: [PATCH 1/2] Btrfs: fix OOPS of empty filesystem after balance
From:       Arne Jansen <sensille () gmx ! net>
Date:       2011-03-30 11:58:50
Message-ID: 4D931AFA.1050004 () gmx ! net
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Am 10.03.2011 13:28, schrieb Chris Mason:
> Excerpts from liubo's message of 2011-03-10 03:50:27 -0500:
>> On 03/07/2011 10:13 AM, liubo wrote:
>>> btrfs will remove unused block groups after balance.
>>> When a empty filesystem is balanced, the block group with tag "DATA" may be
>>> dropped, and after umount and mount again, it will not find "DATA" space_info
>>> and lead to OOPS.
>>> So we initial the necessary space_infos(DATA, SYSTEM, METADATA) to avoid OOPS.
>>>

this patch breaks mixed block groups. If the space_infos get added
upfront, later on all mixed block groups will be added to the data
space_info, leaving the metadata space_info completely empty.
No mixed space_info will ever get created.
As a fix it might be enough to call btrfs_init_space_info after
btrfs_read_block_groups, not before, but I haven't tested it.

This was the cause of the BUG reported by Sergei Trofimovich in the
thread "v2.6.38-6555-ga44f99c: null pointer dereference on -ENOSPC".

-Arne

>>
>> Hi, Chirs,
>>
>> These two fixes are for critical problems(one OOPS and one memory leak), so would
>> you please take some time to review them and check if they are ready for the next
>> git pull? 
>>
>> Seems that you have been a lot busy these days. ;)
> 
> Hi Liubo,
> 
> I'm looking at both of these.  There are no more rc's for 2.6.38, only
> the final release, so the bar is very high for a commit that goes in.
> 
> -chris
> 
>>
>> thanks,
>> liubo
>>
>>> Reported-by: Daniel J Blueman <daniel.blueman@gmail.com>
>>> Signed-off-by: Liu Bo <liubo2009@cn.fujitsu.com>
>>> ---
>>>  fs/btrfs/ctree.h       |    1 +
>>>  fs/btrfs/disk-io.c     |    6 ++++++
>>>  fs/btrfs/extent-tree.c |   23 +++++++++++++++++++++++
>>>  3 files changed, 30 insertions(+), 0 deletions(-)
>>>
>>> diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
>>> index 28188a7..49c50e5 100644
>>> --- a/fs/btrfs/ctree.h
>>> +++ b/fs/btrfs/ctree.h
>>> @@ -2221,6 +2221,7 @@ int btrfs_error_discard_extent(struct btrfs_root *root, u64 bytenr,
>>>                     u64 num_bytes);
>>>  int btrfs_force_chunk_alloc(struct btrfs_trans_handle *trans,
>>>                  struct btrfs_root *root, u64 type);
>>> +int btrfs_init_space_info(struct btrfs_fs_info *fs_info);
>>>  
>>>  /* ctree.c */
>>>  int btrfs_bin_search(struct extent_buffer *eb, struct btrfs_key *key,
>>> diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
>>> index 3e1ea3e..8bcdc62 100644
>>> --- a/fs/btrfs/disk-io.c
>>> +++ b/fs/btrfs/disk-io.c
>>> @@ -1967,6 +1967,12 @@ struct btrfs_root *open_ctree(struct super_block *sb,
>>>      fs_info->metadata_alloc_profile = (u64)-1;
>>>      fs_info->system_alloc_profile = fs_info->metadata_alloc_profile;
>>>  
>>> +    ret = btrfs_init_space_info(fs_info);
>>> +    if (ret) {
>>> +        printk(KERN_ERR "Failed to initial space info: %d\n", ret);
>>> +        goto fail_block_groups;
>>> +    }
>>> +
>>>      ret = btrfs_read_block_groups(extent_root);
>>>      if (ret) {
>>>          printk(KERN_ERR "Failed to read block groups: %d\n", ret);
>>> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
>>> index 100e409..08525ee 100644
>>> --- a/fs/btrfs/extent-tree.c
>>> +++ b/fs/btrfs/extent-tree.c
>>> @@ -8714,6 +8714,29 @@ out:
>>>      return ret;
>>>  }
>>>  
>>> +int btrfs_init_space_info(struct btrfs_fs_info *fs_info)
>>> +{
>>> +    struct btrfs_space_info *space_info;
>>> +    int ret;
>>> +
>>> +    ret = update_space_info(fs_info, BTRFS_BLOCK_GROUP_SYSTEM, 0, 0,
>>> +                                 &space_info);
>>> +    if (ret)
>>> +        return ret;
>>> +
>>> +    ret = update_space_info(fs_info, BTRFS_BLOCK_GROUP_METADATA, 0, 0,
>>> +                                 &space_info);
>>> +    if (ret)
>>> +        return ret;
>>> +
>>> +    ret = update_space_info(fs_info, BTRFS_BLOCK_GROUP_DATA, 0, 0,
>>> +                                 &space_info);
>>> +    if (ret)
>>> +        return ret;
>>> +
>>> +    return ret;
>>> +}
>>> +
>>>  int btrfs_error_unpin_extent_range(struct btrfs_root *root, u64 start, u64 end)
>>>  {
>>>      return unpin_extent_range(root, start, end);
>>
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