Re: [PATCH] xfs: remote attribute overwrite causes transaction overrun

[Dave Chinner <david@fromorbit.com>]

On Tue, Apr 22, 2014 at 08:00:55PM +0800, Jeff Liu wrote:
> 
> On 04/22 2014 14:59 PM, Dave Chinner wrote:
> > From: Dave Chinner <dchinner@redhat.com>
> > 
> > Commit e461fcb ("xfs: remote attribute lookups require the value
> > length") passes the remote attribute length in the xfs_da_args
> > structure on lookup so that CRC calculations and validity checking
> > can be performed correctly by related code. This, unfortunately has
> > the side effect of changing the args->valuelen parameter in cases
> > where it shouldn't.
> > 
> > That is, when we replace a remote attribute, the incoming
> > replacement stores the value and length in args->value and
> > args->valuelen, but then the lookup which finds the existing remote
> > attribute overwrites args->valuelen with the length of the remote
> > attribute being replaced. Hence when we go to create the new
> > attribute, we create it of the size of the existing remote
> > attribute, not the size it is supposed to be. When the new attribute
> > is much smaller than the old attribute, this results in a
> > transaction overrun and an ASSERT() failure on a debug kernel:
> > 
> > XFS: Assertion failed: tp->t_blk_res_used <= tp->t_blk_res, file: fs/xfs/xfs_trans.c, line: 331
> > 
> > Fix this by keeping the remote attribute value length separate to
> > the attribute value length in the xfs_da_args structure. The enables
> > us to pass the length of the remote attribute to be removed without
> > overwriting the new attribute's length.
> > 
> > Signed-off-by: Dave Chinner <dchinner@redhat.com>
....
> > @@ -348,6 +348,11 @@ xfs_attr_rmtval_get(
> >  
> >  	ASSERT(!(args->flags & ATTR_KERNOVAL));
> >  
> > +	/* remote value might be different size to the buffer supplied. */
> > +	if (args->rmtvaluelen = args->valuelen)
> 			     ^^^
> Here is a typo...

Oh, well spotted.

But, hold on a minute, shouldn't gcc be catching those sorts of
typos?

/me groans

$ gcc t.c
$ gcc -Wall t.c
t.c: In function ¿main¿:
t.c:10:2: warning: suggest parentheses around assignment used as truth value [-Wparentheses]
  if (foo = bar)
  ^
$

Only if -Wparentheses is specified.

Why the hell are we suppressing useful warnings on the kernel build?

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com

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