zone_pcp_reset allegedly protects against a race with drain_pages
using local_irq_save but this is bogus. local_irq_save only operates
on the local CPU. If memory hotplug is running on CPU A and drain_pages
is running on CPU B, disabling IRQs on CPU A does not affect CPU B and
offers no protection.
This patch deletes IRQ disable/enable on the grounds that IRQs protect
nothing and assumes the existing hotplug paths guarantees the PCP cannot be
used after zone_pcp_enable(). That should be the case already because all
the pages have been freed and there is no page to put on the PCP lists.
Signed-off-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
---
Resending for email address correction and adding lists
Changelog since v1
o Minimal fix
mm/page_alloc.c | 4 ----
1 file changed, 4 deletions(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 5e8aedb64b57..9bf0db982f14 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -8952,12 +8952,9 @@ void zone_pcp_enable(struct zone *zone)
void zone_pcp_reset(struct zone *zone)
{
- unsigned long flags;
int cpu;
struct per_cpu_pageset *pset;
- /* avoid races with drain_pages() */
- local_irq_save(flags);
if (zone->pageset != &boot_pageset) {
for_each_online_cpu(cpu) {
pset = per_cpu_ptr(zone->pageset, cpu);
@@ -8966,7 +8963,6 @@ void zone_pcp_reset(struct zone *zone)
free_percpu(zone->pageset);
zone->pageset = &boot_pageset;
}
- local_irq_restore(flags);
}
#ifdef CONFIG_MEMORY_HOTREMOVE
