On Thu, 11 May 2023 22:47:36 +0900 Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> wrote:
> 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. 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.
What are the user-visible runtime effects of this flaw?
> Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxx.j
> +++ 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 (unlikely(test_bit(ZONE_BOOSTED_WATERMARK, &zone->flags))
> + && (alloc_flags & ALLOC_KSWAPD)) {
> clear_bit(ZONE_BOOSTED_WATERMARK, &zone->flags);
> wakeup_kswapd(zone, 0, 0, zone_idx(zone));
> }
Thanks, I'll queue this up for some testing while awaiting input from
Mel.
