linux-kernel - Re: "slab: Fix missing DEBUG

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Message-ID: <20110211153524.GB26188@flint.arm.linux.org.uk>
Date:	Fri, 11 Feb 2011 15:35:24 +0000
From:	Russell King <rmk@....linux.org.uk>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Pekka Enberg <penberg@...nel.org>,
	Shiyong Li <shi-yong.li@...orola.com>,
	Linux Kernel List <linux-kernel@...r.kernel.org>,
	David Rientjes <rientjes@...gle.com>
Subject: Re: "slab: Fix missing DEBUG_SLAB last user" breaks ARM

On Fri, Feb 11, 2011 at 09:20:27AM -0600, Christoph Lameter wrote:
> On Fri, 11 Feb 2011, Russell King wrote:
> 
> > On Fri, Feb 11, 2011 at 09:02:45AM +0200, Pekka Enberg wrote:
> > > On Tue, Feb 8, 2011 at 5:02 PM, Christoph Lameter <cl@...ux.com> wrote:
> > > > Uhh.. That first hunk in commit 5c5e3b33b7cb959a401f823707bee006caadd76e
> > > > looks wrong to me. ralign is usually a power of two and greater than
> > > > alignof(unsigned long long). The & operation will result in 0 and never
> > > > exempt any caches.
> > > >
> > > > diff --git a/mm/slab.c b/mm/slab.c
> > > > index bac0f4f..525c664 100644
> > > > --- a/mm/slab.c
> > > > +++ b/mm/slab.c
> > > > @@ -2220,8 +2220,8 @@ kmem_cache_create (const char *name, size_t size,
> > > > size_t align,
> > > >        if (ralign < align) {
> > > >                ralign = align;
> > > >        }
> > > > -       /* disable debug if necessary */
> > > > -       if (ralign > __alignof__(unsigned long long))
> > > > +       /* disable debug if not aligning with REDZONE_ALIGN */
> > > > +       if (ralign & (__alignof__(unsigned long long) - 1))
> > > >                flags &= ~(SLAB_RED_ZONE | SLAB_STORE_USER);
> > > >        /*
> > > >         * 4) Store it.
> > > >
> > > >
> > > > Did you mean
> > > >
> > > >        if (ralign > REDZONE_ALIGN) ...
> > > >
> > > > ?
> > >
> > > Ping. Any arm-capable tester out there that can verify this fix? OTOH,
> > > since Shiyong Li hasn't showed up, I'm inclined to just revert the
> > > commit...
> >
> > What fix?  The above is a quote of the patch in 5c5e3b33.
> 
> He was referring to the change of the if statement.

Replacing what with what?

	if (ralign & (__alignof__(unsigned long long) - 1))
with
	if (ralign > __alignof__(unsigned long long))
or
	if (ralign > REDZONE_ALIGN)

?  A patch is a wonderful way to describe the change to be tested.


-- 
Russell King
 Linux kernel    2.6 ARM Linux   - http://www.arm.linux.org.uk/
 maintainer of:
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