[PATCH] mm/slab: fix cpu on/off handling

From: Joonsoo Kim
Date: Mon Sep 29 2014 - 03:30:43 EST

When cpu off, we flush all cpu cached objects to it's own slab.
free_block() is used for this purpose and it's role is just to flush
objects from array_cache to proper slab. It doesn't adjust array_cache's
internal fields so we should manually reset them to proper value.
Without this fix, we maintain free objects duplicately, one is in
cpu cache, and, the other one is in the slab. So system would be broken.

Reported-by: Jeremiah Mahler <jmmahler@xxxxxxxxx>
Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
mm/slab.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/mm/slab.c b/mm/slab.c
index 1162f0e..ce289b4 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -1102,8 +1102,10 @@ static void cpuup_canceled(long cpu)

/* cpu is dead; no one can alloc from it. */
nc = per_cpu_ptr(cachep->cpu_cache, cpu);
- if (nc)
+ if (nc) {
free_block(cachep, nc->entry, nc->avail, node, &list);
+ nc->avail = 0;
+ }

if (!cpumask_empty(mask)) {

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