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

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Date:	Wed, 13 Jul 2011 10:55:12 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Hugh Dickins <hughd@...gle.com>
cc:	Pekka Enberg <penberg@...nel.org>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH next/mmotm] slub: partly fix freeze in __slab_free


Subject: slub: disable interrupts in cmpxchg_double_slab when falling back to pagelock.

Disable interrupts when falling back to the use of the page lock in
cmpxchg_double_slab().

Becomes necessary since __slab_free will call cmpxchg_double_slab without disabling
interrupts.

A bit bad because the invocations from the allocation path of cmpxchg_double_slab
occur with interrupts already disabled (but there are plans to enable
interrupts there as well in the future).

Signed-off-by: Christoph Lameter <cl@...ux.com>


---
 mm/slub.c |    5 +++++
 1 file changed, 5 insertions(+)

Index: linux-2.6/mm/slub.c
===================================================================
--- linux-2.6.orig/mm/slub.c	2011-07-13 10:51:07.867138834 -0500
+++ linux-2.6/mm/slub.c	2011-07-13 10:51:20.957138752 -0500
@@ -368,14 +368,19 @@ static inline bool cmpxchg_double_slab(s
 	} else
 #endif
 	{
+		unsigned long flags;
+
+		local_irq_save(flags);
 		slab_lock(page);
 		if (page->freelist == freelist_old && page->counters == counters_old) {
 			page->freelist = freelist_new;
 			page->counters = counters_new;
 			slab_unlock(page);
+			local_irq_restore(flags);
 			return 1;
 		}
 		slab_unlock(page);
+		local_irq_restore(flags);
 	}

 	cpu_relax();
--
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