linux-kernel - Re: [percpu] BUG: using __this_cpu_add() in preemptible [00000000] code: init/1

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Date:	Tue, 18 Mar 2014 09:43:27 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Fengguang Wu <fengguang.wu@...el.com>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Pekka Enberg <penberg@...nel.org>
Subject: Re: [percpu]  BUG: using __this_cpu_add() in preemptible [00000000]
 code: init/1

Anyways the statistics in slub should be low impact and able to
be placed anywhere. So I think we need this patch to avoid
the preemption checks begin triggered.

Subject: SLUB: Use raw_cpu_inc for incrementing statistics

Statistics are not critical to the operation of the allocation
but should also not cause too much overhead.

__this_cpu_inc now checks if preemption is disabled and triggers.
Use raw_cpu_inc to avoid the checks. Using this_cpu_ops may cause
interrupt disable/enable sequences on various arches which may
significantly impact allocator performance.

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

Index: linux/mm/slub.c
===================================================================
--- linux.orig/mm/slub.c	2014-03-07 14:10:30.142777022 -0600
+++ linux/mm/slub.c	2014-03-18 09:39:15.675035324 -0500
@@ -224,7 +224,7 @@
 static inline void stat(const struct kmem_cache *s, enum stat_item si)
 {
 #ifdef CONFIG_SLUB_STATS
-	__this_cpu_inc(s->cpu_slab->stat[si]);
+	raw_cpu_inc(s->cpu_slab->stat[si]);
 #endif
 }

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