mm/page_alloc: don't wake kswapd from rmqueue() unless __GFP_KSWAPD_RECLAIM is specified

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.

Link: https://lkml.kernel.org/r/c3c3dacf-dd3b-77c9-f96a-d0982b4b2a4f@I-love.SAKURA.ne.jp
Fixes: 73444bc4d8f9 ("mm, page_alloc: do not wake kswapd with zone lock held")
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Acked-by: Mel Gorman <mgorman@techsingularity.net>
Cc: "Huang, Ying" <ying.huang@intel.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 7e8673504a3d36edcf29c123eb0bf2141ebb9bd4..091a6cb44265fc19a238ad98c78cdf2d99869677 100644 (file)
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2827,7 +2827,8 @@ 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));
        }