The patch below does not apply to the 6.6-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.6.y git checkout FETCH_HEAD git cherry-pick -x 66eca1021a42856d6af2a9802c99e160278aed91 # <resolve conflicts, build, test, etc.> git commit -s git send-email --to 'stable@vger.kernel.org' --in-reply-to '2024072902-yippee-superbowl-f065@gregkh' --subject-prefix 'PATCH 6.6.y' HEAD^..

Possible dependencies:

66eca1021a42 ("mm/page_alloc: fix pcp->count race between drain_pages_zone() vs __rmqueue_pcplist()") 55f77df7d715 ("mm: page_alloc: control latency caused by zone PCP draining")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 66eca1021a42856d6af2a9802c99e160278aed91 Mon Sep 17 00:00:00 2001 From: Li Zhijian lizhijian@fujitsu.com Date: Tue, 23 Jul 2024 14:44:28 +0800 Subject: [PATCH] mm/page_alloc: fix pcp->count race between drain_pages_zone() vs __rmqueue_pcplist()

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@fujits...

Link: https://lkml.kernel.org/r/20240723064428.1179519-1-lizhijian@fujitsu.com Fixes: 4b23a68f9536 ("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

diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 7ac8d61148fe..28f80daf5c04 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -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); - 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); }

/*