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

[Dave Chinner <david@fromorbit.com>]

On Wed, Apr 23, 2014 at 09:46:28AM +1000, Dave Chinner wrote:
> 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?

Hmmm - looks like I missed the output of the warning when I built
against 3.15-rc2 because it was a rebuild the world and there's tons
of output when that happens...

<sigh>

Time to add ccflags-y += -Werror to the makefile....

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com

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