The patch titled
Subject: mm/memory_hotplug: remove broken locking of zone PCP structures during hot remove
has been removed from the -mm tree. Its filename was
mm-memory_hotplug-make-unpopulated-zones-pcp-structures-unreachable-during-hot-remove.patch
This patch was dropped because it was merged into mainline or a subsystem tree
------------------------------------------------------
From: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Subject: 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@xxxxxxxxxxxxxxxxxxx
Signed-off-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Reviewed-by: Oscar Salvador <osalvador@xxxxxxx>
Cc: "Michael S. Tsirkin" <mst@xxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/page_alloc.c | 4 ----
1 file changed, 4 deletions(-)
--- a/mm/page_alloc.c~mm-memory_hotplug-make-unpopulated-zones-pcp-structures-unreachable-during-hot-remove
+++ a/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
_
Patches currently in -mm which might be from mgorman@xxxxxxxxxxxxxxxxxxx are
