In pageset_set_batch() and setup_pagelist_highmark(), ensure that batch
is always set to a safe value (1) prior to updating high, and ensure
that high is fully updated before setting the real value of batch.
Suggested by Gilad Ben-Yossef <gi...@benyossef.com> in this thread:
https://lkml.org/lkml/2013/4/9/23
Also reproduces his proposed comment.
Signed-off-by: Cody P Schafer <c...@linux.vnet.ibm.com>
---
mm/page_alloc.c | 19 +++++++++++++++++++
1 file changed, 19 insertions(+)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index d259599..a07bd4c 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -4007,11 +4007,26 @@ static int __meminit zone_batchsize(struct zone *zone)
#endif
}
+static void pageset_update_prep(struct per_cpu_pages *pcp)
+{
+ /*
+ * We're about to mess with PCP in an non atomic fashion. Put an
+ * intermediate safe value of batch and make sure it is visible before
+ * any other change
+ */
+ pcp->batch = 1;
+ smp_wmb();
+}
+
/* a companion to setup_pagelist_highmark() */
static void pageset_set_batch(struct per_cpu_pageset *p, unsigned long batch)
{
struct per_cpu_pages *pcp = &p->pcp;
+ pageset_update_prep(pcp);
+
pcp->high = 6 * batch;
+ smp_wmb();
+
pcp->batch = max(1UL, 1 * batch);
}
@@ -4039,7 +4054,11 @@ static void setup_pagelist_highmark(struct
per_cpu_pageset *p,
struct per_cpu_pages *pcp;
pcp = &p->pcp;
+ pageset_update_prep(pcp);
+
pcp->high = high;
+ smp_wmb();
+
pcp->batch = max(1UL, high/4);
if ((high/4) > (PAGE_SHIFT * 8))
pcp->batch = PAGE_SHIFT * 8;
--
1.8.2
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