linux-kernel - Re: [PATCH SLAB 1/2 v3] duplicate the cache name in SLUB's saved

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Date:	Mon, 9 Jul 2012 09:01:12 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Li Zhong <zhong@...ux.vnet.ibm.com>
cc:	LKML <linux-kernel@...r.kernel.org>,
	Pekka Enberg <penberg@...nel.org>,
	Matt Mackall <mpm@...enic.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	linux-mm <linux-mm@...ck.org>,
	PowerPC email list <linuxppc-dev@...ts.ozlabs.org>,
	Wanlong Gao <gaowanlong@...fujitsu.com>,
	Glauber Costa <glommer@...allels.com>
Subject: Re: [PATCH SLAB 1/2 v3] duplicate the cache name in SLUB's saved_alias
 list, SLAB, and SLOB


> I was pointed by Glauber to the slab common code patches. I need some
> more time to read the patches. Now I think the slab/slot changes in this
> v3 are not needed, and can be ignored.

That may take some kernel cycles. You have a current issue here that needs
to be fixed.

> >  	down_write(&slub_lock);
> > -	s = find_mergeable(size, align, flags, name, ctor);
> > +	s = find_mergeable(size, align, flags, n, ctor);
> >  	if (s) {
> >  		s->refcount++;
> >  		/*
>
> 		......
> 		up_write(&slub_lock);
> 		return s;
> 	}
>
> Here, the function returns without name string n be kfreed.

That is intentional since the string n is still referenced by the entry
that sysfs_slab_alias has created.

> But we couldn't kfree n here, because in sysfs_slab_alias(), if
> (slab_state < SYS_FS), the name need to be kept valid until
> slab_sysfs_init() is finished adding the entry into sysfs.

Right that is why it is not freed and that is what fixes the issue you
see.
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