From: Mel Gorman <mgorman@techsingularity.net>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Oscar Salvador <osalvador@suse.de>,
"Michael S. Tsirkin" <mst@redhat.com>,
Vlastimil Babka <vbabka@suse.cz>,
Alexander Duyck <alexanderduyck@fb.com>,
Minchan Kim <minchan@kernel.org>, Michal Hocko <mhocko@suse.com>,
David Hildenbrand <david@redhat.com>,
Linux-MM <linux-mm@kvack.org>,
LKML <linux-kernel@vger.kernel.org>
Subject: [PATCH v2 resend] mm/memory_hotplug: Make unpopulated zones PCP structures unreachable during hot remove
Date: Mon, 12 Apr 2021 13:08:42 +0100 [thread overview]
Message-ID: <20210412120842.GY3697@techsingularity.net> (raw)
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@techsingularity.net>
---
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
next reply other threads:[~2021-04-12 12:08 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-12 12:08 Mel Gorman [this message]
2021-04-12 12:12 ` [PATCH v2 resend] mm/memory_hotplug: Make unpopulated zones PCP structures unreachable during hot remove David Hildenbrand
2021-04-12 12:40 ` Vlastimil Babka
2021-04-12 14:08 ` Mel Gorman
2021-04-12 14:12 ` David Hildenbrand
2021-04-12 15:27 ` Mel Gorman
2021-04-12 16:02 ` David Hildenbrand
2021-04-13 9:36 ` Vlastimil Babka
2021-04-13 9:49 ` Mel Gorman
2021-04-13 10:16 ` Michal Hocko
2021-04-13 6:44 ` Michal Hocko
2021-04-13 6:40 ` Michal Hocko
2021-04-14 7:18 ` Oscar Salvador
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