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mm/page_alloc: fix pcp->count race between drain_pages_zone() vs __rmqueue_pcplist()

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It's expected that no page should be left in pcp_list after calling
zone_pcp_disable() in offline_pages().  Previously, it's observed that
offline_pages() gets stuck [1] due to some pages remaining in pcp_list.

Cause:
There is a race condition between drain_pages_zone() and __rmqueue_pcplist()
involving the pcp->count variable. See below scenario:

         CPU0                              CPU1
    ----------------                    ---------------
                                      spin_lock(&pcp->lock);
                                      __rmqueue_pcplist() {
zone_pcp_disable() {
                                        /* list is empty */
                                        if (list_empty(list)) {
                                          /* add pages to pcp_list */
                                          alloced = rmqueue_bulk()
  mutex_lock(&pcp_batch_high_lock)
  ...
  __drain_all_pages() {
    drain_pages_zone() {
      /* read pcp->count, it's 0 here */
      count = READ_ONCE(pcp->count)
      /* 0 means nothing to drain */
                                          /* update pcp->count */
                                          pcp->count += alloced << order;
      ...
                                      ...
                                      spin_unlock(&pcp->lock);

In this case, after calling zone_pcp_disable() though, there are still some
pages in pcp_list. And these pages in pcp_list are neither movable nor
isolated, offline_pages() gets stuck as a result.

Solution:
Expand the scope of the pcp->lock to also protect pcp->count in
drain_pages_zone(), to ensure no pages are left in the pcp list after
zone_pcp_disable()

[1] https://lore.kernel.org/linux-mm/6a07125f-e720-404c-b2f9-e55f3f166e85@fujitsu.com/

Link: https://lkml.kernel.org/r/20240723064428.1179519-1-lizhijian@fujitsu.com
Fixes: 4b23a68f95 ("mm/page_alloc: protect PCP lists with a spinlock")
Signed-off-by: Li Zhijian <lizhijian@fujitsu.com>
Reported-by: Yao Xingtao <yaoxt.fnst@fujitsu.com>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Cc: David Hildenbrand <david@redhat.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Li Zhijian 2024-07-23 14:44:28 +08:00 committed by Andrew Morton
parent f59adcf593
commit 66eca1021a
1 changed files with 11 additions and 7 deletions
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16
mm/page_alloc.c
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@ -2343,16 +2343,20 @@ void drain_zone_pages(struct zone *zone, struct per_cpu_pages *pcp)
static void drain_pages_zone(unsigned int cpu, struct zone *zone)
{
struct per_cpu_pages *pcp = per_cpu_ptr(zone->per_cpu_pageset, cpu);
int count = READ_ONCE(pcp->count);
while (count) {
int to_drain = min(count, pcp->batch << CONFIG_PCP_BATCH_SCALE_MAX);
count -= to_drain;
int count;
do {
spin_lock(&pcp->lock);
count = pcp->count;
if (count) {
int to_drain = min(count,
pcp->batch << CONFIG_PCP_BATCH_SCALE_MAX);
free_pcppages_bulk(zone, to_drain, pcp, 0);
spin_unlock(&pcp->lock);
count -= to_drain;
}
spin_unlock(&pcp->lock);
} while (count);
}
/*