diff mbox series

[124/143] mm/memory_hotplug: remove broken locking of zone PCP structures during hot remove

Message ID 20210505013930.bzriZCvbx%akpm@linux-foundation.org (mailing list archive)
State New
Headers show
Series [001/143] mm: introduce and use mapping_empty() | expand

Commit Message

Andrew Morton May 5, 2021, 1:39 a.m. UTC
From: Mel Gorman <mgorman@techsingularity.net>
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

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>

 mm/page_alloc.c |    4 ----
 1 file changed, 4 deletions(-)
diff mbox series


--- 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)
 		zone->pageset = &boot_pageset;
-	local_irq_restore(flags);