Commit 73444bc4d8f9 ("mm, page_alloc: do not wake kswapd with zone lock
held") moved wakeup_kswapd() from steal_suitable_fallback() to rmqueue()
using ZONE_BOOSTED_WATERMARK flag.
Only allocation contexts that include ALLOC_KSWAPD (which corresponds to
__GFP_KSWAPD_RECLAIM) should wake kswapd, for callers are supposed to
remove __GFP_KSWAPD_RECLAIM if trying to hold pgdat->kswapd_wait has a
risk of deadlock. But since zone->flags is a shared variable, a thread
doing !__GFP_KSWAPD_RECLAIM allocation request might observe this flag
being set immediately after another thread doing __GFP_KSWAPD_RECLAIM
allocation request set this flag, causing possibility of deadlock.
Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Fixes: 73444bc4d8f9 ("mm, page_alloc: do not wake kswapd with zone lock held")
---
Changes in v2:
Check ALLOC_KSWAPD before checking ZONE_BOOSTED_WATERMARK and update
description, suggested by Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>.
mm/page_alloc.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 47421bedc12b..ecad680cec53 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3052,7 +3052,8 @@ struct page *rmqueue(struct zone *preferred_zone,
out:
/* Separate test+clear to avoid unnecessary atomics */
- if (unlikely(test_bit(ZONE_BOOSTED_WATERMARK, &zone->flags))) {
+ if ((alloc_flags & ALLOC_KSWAPD) &&
+ unlikely(test_bit(ZONE_BOOSTED_WATERMARK, &zone->flags))) {
clear_bit(ZONE_BOOSTED_WATERMARK, &zone->flags);
wakeup_kswapd(zone, 0, 0, zone_idx(zone));
}
--
2.18.4
