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Re: [PATCH 2/3] xfs: fix implicit padding in directory and attr CRC form

To: Ben Myers <bpm@xxxxxxx>
Subject: Re: [PATCH 2/3] xfs: fix implicit padding in directory and attr CRC formats
From: "Michael L. Semon" <mlsemon35@xxxxxxxxx>
Date: Wed, 12 Jun 2013 21:40:47 -0400
Cc: Dave Chinner <david@xxxxxxxxxxxxx>, xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
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On 06/12/2013 08:58 PM, Ben Myers wrote:
> On Wed, Jun 12, 2013 at 12:19:07PM +1000, Dave Chinner wrote:
>> From: Dave Chinner <dchinner@xxxxxxxxxx>
>> Michael L. Semon has been testing CRC patches ona 32 bit system and
>                                               on a
>> been seeing assert failures in the directory code from xfs/080.
>> Thanks to Michael's heroic efforts with printk debugging, we found
>> that the problem was that the last free space being left in the
>> directory structure was too small to fit a unused tag structure and
>> it was being corrupted and attempting to log a region out of bounds.
>> Hence the assert failure looked something like:
>> .....
>> #5 calling xfs_dir2_data_log_unused() 36 32
>> #1 4092 4095 4096
>> #2 8182 8183 4096
>      first? 
>           last?
>                bp->b_length?


This is all terrible numbering on my part...

>> #1 4092 4095 4096
>> #2 8182 8183 4096

xfs_dir2_data_log_unused() calls xfs_trans_log_buf() twice in the same 
function.  #1 is the first call, #2 is the second call, and there's no 
running count.  The printk() is a copy-and-paste of those two function 
calls plus a BBTOB(bp->b_length) below it.

>> #5 calling xfs_dir2_data_log_unused() 36 32

The #5 was caused by numbering all the calls to 
xfs_dir2_data_log_unused() to see if one code path was being called 
every time.  #5 is in the xfs_dir2_data_use_free() function, starting 
with this else-if...

        else if (matchfront) {
                newdup = (xfs_dir2_data_unused_t *)((char *)hdr + offset + len);
                newdup->freetag = cpu_to_be16(XFS_DIR2_DATA_FREE_TAG);
                newdup->length = cpu_to_be16(oldlen - len);
                *xfs_dir2_data_unused_tag_p(newdup) =
                        cpu_to_be16((char *)newdup - (char *)hdr);
                printk( KERN_INFO "#5 calling xfs_dir2_data_log_unused() %d 
%d\n", oldlen, len );
                xfs_dir2_data_log_unused(tp, bp, newdup);

Sorry about that!


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