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Re: [PATCH] xfs_repair: zero out unused parts of superblocks

To: Eric Sandeen <sandeen@xxxxxxxxxx>
Subject: Re: [PATCH] xfs_repair: zero out unused parts of superblocks
From: Rich Johnston <rjohnston@xxxxxxx>
Date: Tue, 27 Aug 2013 12:47:10 -0500
Cc: Michael Maier <m1278468@xxxxxxxxxxx>, xfs-oss <xfs@xxxxxxxxxxx>
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <520E3FBF.7070708@xxxxxxxxxx>
References: <520C3C60.3090500@xxxxxxxxxx> <520D0A15.1050304@xxxxxxxxxxx> <520E3FBF.7070708@xxxxxxxxxx>
User-agent: Mozilla/5.0 (X11; Linux i686; rv:17.0) Gecko/20130329 Thunderbird/17.0.5
On 08/16/2013 10:05 AM, Eric Sandeen wrote:
On 8/15/13 12:04 PM, Michael Maier wrote:
Eric Sandeen wrote:
Prior to:
1375cb65 xfs: growfs: don't read garbage for new secondary superblocks

we ran the risk of allowing garbage in secondary superblocks
beyond the in-use sb fields.  With kernels 3.10 and beyond, the
verifiers will kick these out as invalid, but xfs_repair does
not detect or repair this condition.

There is superblock stale-data zeroing code, but it is under a
narrow conditional - the bug addressed in the above commit did not
meet that conditional.  So change this to check unconditionally.

Further, the checking code was looking at the in-memory
superblock buffer, which was zeroed prior to population, and
would therefore never possibly show any stale data beyond the
last up-rev superblock field.

So instead, check the disk buffer for this garbage condition.

If we detect garbage, we must zero out both the in-memory sb
and the disk buffer; the former may contain unused data
in up-rev sb fields which will be written back out; the latter
may contain garbage beyond all fields, which won't be updated
when we translate the in-memory sb back to disk.

The V4 superblock case was zeroing out the sb_bad_features2
field; we also fix that to leave that field alone.

Lastly, use offsetof() instead of the tortured (__psint_t)
casts & pointer math.

Reported-by: Michael Maier <m1278468@xxxxxxxxxxx>
Signed-off-by: Eric Sandeen <sandeen@xxxxxxxxxx>

Michael - this will need slight tweaking to apply against
older xfsprogs.


With more of Dave's changes, I think we can swap out:

                size = offsetof(xfs_sb_t, sb_lsn)
                        + sizeof(sb->sb_lsn);
                size = xfs_sb_info[XFS_SBS_LSN + 1].offset;

but this version is a bit easier to backport, and works in the
current git tree...

I tested with current git tree and it worked as expected for me!
Afterwards I was able to run xfs_growfs (from 3.1.11) w/o any problem.

Please excuse me - forgot to set the english locale before starting.
Hope you can guess what it should be in english :-).

Kein Problem, ich kann etwas Deutsch zu lesen. :)

Ich auch :)

Code looks good.
Reviewed-by: Rich Johnston <rjohnston@xxxxxxx>

Glad it worked for you!


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