[PATCH] mm/page_alloc: add cond_resched in __drain_all_pages()

[mengensun88@gmail.com]

From: MengEn Sun <mengensun@tencent.com>

Since version v5.19-rc7, draining remote per-CPU pools (PCP) no
longer relies on workqueues; instead, the current CPU is
responsible for draining the PCPs of all CPUs.

However, due to the lack of scheduling points in the
__drain_all_pages function, this can lead to soft locks in
some extreme cases.

We observed the following soft-lockup stack on a 64-core,
223GB machine during testing:
watchdog: BUG: soft lockup - CPU#29 stuck for 23s! [stress-ng-vm]
RIP: 0010:native_queued_spin_lock_slowpath+0x5b/0x1c0
_raw_spin_lock
drain_pages_zone
drain_pages
drain_all_pages
__alloc_pages_slowpath
__alloc_pages_nodemask
alloc_pages_vma
do_huge_pmd_anonymous_page
handle_mm_fault

Fixes: <443c2accd1b66> ("mm/page_alloc: remotely drain per-cpu lists")
Reviewed-by: JinLiang Zheng <alexjlzheng@tencent.com>
Signed-off-by: MengEn Sun <mengensun@tencent.com>
---
 mm/page_alloc.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index c6c7bb3ea71b..d05b32ec1e40 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2487,6 +2487,7 @@ static void __drain_all_pages(struct zone *zone, bool force_all_cpus)
 			drain_pages_zone(cpu, zone);
 		else
 			drain_pages(cpu);
+		cond_resched();
 	}
 
 	mutex_unlock(&pcpu_drain_mutex);
-- 
2.43.5