+ mm-page_alloc-fix-pcp-count-race-between-drain_pages_zone-vs-__rmqueue_pcplist.patch added to mm-hotfixes-unstable branch

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



The patch titled
     Subject: mm/page_alloc: fix pcp->count race between drain_pages_zone() vs __rmqueue_pcplist()
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     mm-page_alloc-fix-pcp-count-race-between-drain_pages_zone-vs-__rmqueue_pcplist.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-page_alloc-fix-pcp-count-race-between-drain_pages_zone-vs-__rmqueue_pcplist.patch

This patch will later appear in the mm-hotfixes-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days

------------------------------------------------------
From: Li Zhijian <lizhijian@xxxxxxxxxxx>
Subject: mm/page_alloc: fix pcp->count race between drain_pages_zone() vs __rmqueue_pcplist()
Date: Tue, 23 Jul 2024 14:44:28 +0800

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@xxxxxxxxxxx/

Link: https://lkml.kernel.org/r/20240723064428.1179519-1-lizhijian@xxxxxxxxxxx
Fixes: 4b23a68f9536 ("mm/page_alloc: protect PCP lists with a spinlock")
Signed-off-by: Li Zhijian <lizhijian@xxxxxxxxxxx>
Reported-by: Yao Xingtao <yaoxt.fnst@xxxxxxxxxxx>
Reviewed-by: Vlastimil Babka <vbabka@xxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 mm/page_alloc.c |   18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

--- a/mm/page_alloc.c~mm-page_alloc-fix-pcp-count-race-between-drain_pages_zone-vs-__rmqueue_pcplist
+++ a/mm/page_alloc.c
@@ -2343,16 +2343,20 @@ void drain_zone_pages(struct zone *zone,
 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);
-		free_pcppages_bulk(zone, to_drain, pcp, 0);
+		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);
+			count -= to_drain;
+		}
 		spin_unlock(&pcp->lock);
-	}
+	} while (count);
 }
 
 /*
_

Patches currently in -mm which might be from lizhijian@xxxxxxxxxxx are

mm-page_alloc-fix-pcp-count-race-between-drain_pages_zone-vs-__rmqueue_pcplist.patch





[Index of Archives]     [Kernel Archive]     [IETF Annouce]     [DCCP]     [Netdev]     [Networking]     [Security]     [Bugtraq]     [Yosemite]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Linux RAID]     [Linux SCSI]

  Powered by Linux