linux-kernel - Re: [PATCH next/mmotm] slub: partly fix freeze in __slab

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Date:	Mon, 11 Jul 2011 21:39:27 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Hugh Dickins <hughd@...gle.com>
Cc:	Christoph Lameter <cl@...ux.com>,
	Pekka Enberg <penberg@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH next/mmotm] slub: partly fix freeze in __slab_free

Le lundi 11 juillet 2011 à 11:58 -0700, Hugh Dickins a écrit :
> My load tests on PowerPC freeze within minutes in __slab_free().
> I happened to try PPC first, didn't try without this fix on x86.
> 
> It looks as if the author was interrupted while devising the new
> cmpxchg_double_slab() version of __slab_free(): its decision to
> spin_lock_irqsave() depends on several uninitialized fields,
> and fixing that (by copying page to new) mostly fixes it.
> 
> But I didn't think about it very much, and this may well not be what
> the author intends; and I have seen a couple of much rarer freezes
> in __slab_free() on PPC (not yet on x86) even after applying this.
> 
> Signed-off-by: Hugh Dickins <hughd@...gle.com>
> ---
>  mm/slub.c |    1 +
>  1 file changed, 1 insertion(+)
> 
> --- mmotm/mm/slub.c	2011-07-08 18:59:44.135443127 -0700
> +++ linux/mm/slub.c	2011-07-10 05:07:08.000000000 -0700
> @@ -2217,6 +2217,7 @@ static void __slab_free(struct kmem_cach
>  		return;
>  
>  	do {
> +		new = *page;
>  		prior = page->freelist;
>  		counters = page->counters;
>  		set_freepointer(s, object, prior);
> --

I suspect you hit the bug on 32bit arch ?

What about following patch instead ?

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 3d76a43..1351d28 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -62,7 +62,7 @@ struct page {
 		struct {			/* SLUB cmpxchg_double area */
 			void *freelist;
 			union {
-				unsigned long counters;
+				u64	counters;
 				struct {
 					unsigned inuse:16;
 					unsigned objects:15;


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