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Re: [PATCH] xfs: limit superblock corruption errors to probable corrupti

To: Dave Chinner <david@xxxxxxxxxxxxx>, Brian Foster <bfoster@xxxxxxxxxx>
Subject: Re: [PATCH] xfs: limit superblock corruption errors to probable corruption
From: Eric Sandeen <sandeen@xxxxxxxxxxx>
Date: Thu, 06 Feb 2014 22:23:48 -0600
Cc: Eric Sandeen <sandeen@xxxxxxxxxx>, xfs-oss <xfs@xxxxxxxxxxx>
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <20140206064314.GM13997@dastard>
References: <52E88D8B.90208@xxxxxxxxxx> <52EAB56D.2050203@xxxxxxxxxx> <52EAB66E.204@xxxxxxxxxx> <52EABBF8.5070309@xxxxxxxxxx> <20140206064314.GM13997@dastard>
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On 2/6/14, 12:43 AM, Dave Chinner wrote:
> On Thu, Jan 30, 2014 at 03:54:16PM -0500, Brian Foster wrote:
>> On 01/30/2014 03:30 PM, Eric Sandeen wrote:
>>> On 1/30/14, 2:26 PM, Brian Foster wrote:
>>>>> diff --git a/fs/xfs/xfs_sb.c b/fs/xfs/xfs_sb.c
>>>>>> index 511cce9..b575317 100644
>>>>>> --- a/fs/xfs/xfs_sb.c
>>>>>> +++ b/fs/xfs/xfs_sb.c
>>>>>> @@ -617,6 +617,8 @@ xfs_sb_read_verify(
>>>>>>                          /* Only fail bad secondaries on a known V5 
>>>>>> filesystem */
>>>>>>                          if (bp->b_bn != XFS_SB_DADDR &&
>>>>>>                              xfs_sb_version_hascrc(&mp->m_sb)) {
>>>>>> +                                XFS_CORRUPTION_ERROR(__func__, 
>>>>>> XFS_ERRLEVEL_LOW,
>>>>>> +                                                     mp, bp->b_addr);
>>>>>>                                  error = EFSCORRUPTED;
>>>>>>                                  goto out_error;
>>>>>>                          }
>>>>>> @@ -625,12 +627,8 @@ xfs_sb_read_verify(
>>>>>>          error = xfs_sb_verify(bp, true);
>>>>>>  
>>>>>>  out_error:
>>>>>> -        if (error) {
>>>>>> -                if (error != EWRONGFS)
>>>>>> -                        XFS_CORRUPTION_ERROR(__func__, XFS_ERRLEVEL_LOW,
>>>>>> -                                             mp, bp->b_addr);
>>>>>> +        if (error)
>>>>>>                  xfs_buf_ioerror(bp, error);
>>>>>> -        }
>>>>>>  }
>>>> ... but why not leave the corruption output here in out_error, change
>>>> the check to (error == EFSCORRUPTED) and remove the now duplicate
>>>> corruption message in xfs_mount_validate_sb() (or replace it with a
>>>> warn/notice message)? This would catch the other EFSCORRUPTED returns in
>>>> a consistent manner, including another potential duplicate in the write
>>>> verifier. I guess we'd lose a little specificity between the crc failure
>>>> and sb validation, but we could add a warn/notice for the former too.
>>>>
>>>> Brian
>>>>
>>>
>>> Well, I went back and forth on this.  It's probably philosophical. ;)
>>>
>>> Should we emit the corruption error at the point of corruption detection,
>>> or at a higher level?  I guess my concern was that while *this* caller
>>> might catch the return & yell, if another caller got added it might not.
>>>
>>> Putting it at the point of detection seemed foolproof in that regard.
>>>
>>
>> Yeah, that makes sense too. If we were consistent, that model would
>> suggest the write verifier corruption message could go and we'd embed
>> corruption errors along with the other associated EFSCORRUPTED returns
>> (at least where the resulting message is appropriate) in
>> xfs_mount_validate_sb().
>>
>> Either way seems reasonable to me. I guess if all the remaining
>> situations are in fact real corruption situations, the point of
>> detection approach is probably more resilient. It would still be nice to
>> make the verifiers consistent in that though. ;)
> 
> And the conclusion to this discussion is ...?

I think Brian has some valid points, I'll take another look at it.

Thanks,
-Eric

> Cheers,
> 
> Dave.
> 

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