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

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Message-ID: <alpine.LSU.2.00.1107111156310.13035@sister.anvils>
Date:	Mon, 11 Jul 2011 11:58:41 -0700 (PDT)
From:	Hugh Dickins <hughd@...gle.com>
To:	Christoph Lameter <cl@...ux.com>
cc:	Pekka Enberg <penberg@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: [PATCH next/mmotm] slub: partly fix freeze in __slab_free

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);
--
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