Re: Internal error xfs_sb_read_verify at line 726

[Eric Sandeen <sandeen@sandeen.net>]

On 5/6/13 1:30 PM, Markus Trippelsdorf wrote:
> On 2013.05.06 at 12:04 -0500, Eric Sandeen wrote:
>> On 5/6/13 6:27 AM, Markus Trippelsdorf wrote:
>>> Today I accidentally tried to mount my backup disk at /dev/sdc instead
>>> of /dev/sdc1 and this is what happened:
>>>
>>> ...
>>> EXT4-fs (sdc): VFS: Can't find ext4 filesystem
>>> FAT-fs (sdc): bogus number of reserved sectors
>>> FAT-fs (sdc): Can't find a valid FAT filesystem
>>> FAT-fs (sdc): bogus number of reserved sectors
>>> FAT-fs (sdc): Can't find a valid FAT filesystem
>>> ISOFS: Unable to identify CD-ROM format.
>>> XFS (sdc): bad magic number
>>> ffff8800db620000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
>>> ffff8800db620010: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
>>> ffff8800db620020: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
>>> ffff8800db620030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
>>> XFS (sdc): Internal error xfs_sb_read_verify at line 726 of file fs/xfs/xfs_mount.c.  Caller 0xffffffff8119e5cd
>>
>> This seems to be a recent regression.
>>
>> Comments above xfs_sb_quiet_read_verify() indicate that this behavior is
>> to be avoided:
>>
>>  * We may be probed for a filesystem match, so we may not want to emit
>>  * messages when the superblock buffer is not actually an XFS superblock.
>>
>> and it checks for proper magic prior to all the chattiness above int
>> that function.
>>
>> The superblock read is suposed to choose whether to be noisy or not,
>> in xfs_readsb():
>>
> 
> The following patch fixes the issue for me:
> 
> 
> diff --git a/fs/xfs/xfs_mount.c b/fs/xfs/xfs_mount.c
> index f6bfbd7..db8f27f 100644
> --- a/fs/xfs/xfs_mount.c
> +++ b/fs/xfs/xfs_mount.c
> @@ -721,6 +721,11 @@ xfs_sb_read_verify(
>  	}
>  	error = xfs_sb_verify(bp);
>  
> +	if (error == XFS_ERROR(EWRONGFS)) {
> +		xfs_buf_ioerror(bp, EWRONGFS);
> +		return;
> +	}
> +
>  out_error:
>  	if (error) {
>  		XFS_CORRUPTION_ERROR(__func__, XFS_ERRLEVEL_LOW, mp, bp->b_addr);

That might make sense, I don't think we need the loudness for EWRONGFS
no matter how we got there.  

But:

Out of curiosity, what was the actual mount command you used?  It seems like
the auto-probing should have set the MS_SILENT flag to avoid this in
the first place, i.e. we should have gone down the quiet path
(xfs_sb_quiet_read_verify) and avoided this altogether.

How do you reproduce this?


If I were to patch xfs_read_sb_verify, I'd probably do it like this:

diff --git a/fs/xfs/xfs_mount.c b/fs/xfs/xfs_mount.c
index f6bfbd7..7488335 100644
--- a/fs/xfs/xfs_mount.c
+++ b/fs/xfs/xfs_mount.c
@@ -723,7 +723,9 @@ xfs_sb_read_verify(
 
 out_error:
 	if (error) {
-		XFS_CORRUPTION_ERROR(__func__, XFS_ERRLEVEL_LOW, mp, bp->b_addr);
+		if (error != EWRONGFS)
+			XFS_CORRUPTION_ERROR(__func__, XFS_ERRLEVEL_LOW,
+					     mp, bp->b_addr);
 		xfs_buf_ioerror(bp, error);
 	}
 }

Because it keeps a single return point in the function, and . . .

XFS_ERROR() is never used on the right side of a test; it's only to turn an error
return into a BUG_ON for certain error numbers when they're set; i.e. it'd
fire in xfs_mount_validate_sb before we ever got to the caller:

                xfs_warn(mp, "bad magic number");
                return XFS_ERROR(EWRONGFS); /* would BUG if configured to do so */

Thanks,
-Eric

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