From 8ca559132a2d9b56732d35e2b947af96acb9b80b Mon Sep 17 00:00:00 2001
From: Mel Gorman <mgorman@techsingularity.net>
Date: Tue, 4 May 2021 18:39:30 -0700
Subject: [PATCH] mm/memory_hotplug: remove broken locking of zone PCP
structures during hot remove
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.
Link: https://lkml.kernel.org/r/20210412090346.GQ3697@techsingularity.net
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Acked-by: Michal Hocko <mhocko@suse.com>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Alexander Duyck <alexander.h.duyck@linux.intel.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: David Hildenbrand <david@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
mm/page_alloc.c | 4 ----
1 file changed, 4 deletions(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 81db389262661..b012805a11ad4 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -9020,12 +9020,9 @@ 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);
@@ -9034,7 +9031,6 @@ void zone_pcp_reset(struct zone *zone)
free_percpu(zone->pageset);
zone->pageset = &boot_pageset;
}
- local_irq_restore(flags);
}
#ifdef CONFIG_MEMORY_HOTREMOVE
--
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