Re: [PATCH] mm/page_alloc.c: Avoid infinite retries caused by cpuset race

[Harry Yoo <harry.yoo@oracle.com>]

On Wed, Apr 16, 2025 at 04:24:05PM +0800, Tianyang Zhang wrote:
> __alloc_pages_slowpath has no change detection for ac->nodemask
> in the part of retry path, while cpuset can modify it in parallel.
> For some processes that set mempolicy as MPOL_BIND, this results
> ac->nodemask changes, and then the should_reclaim_retry will
> judge based on the latest nodemask and jump to retry, while the
> get_page_from_freelist only traverses the zonelist from
> ac->preferred_zoneref, which selected by a expired nodemask
> and may cause infinite retries in some cases
> 
> cpu 64:
> __alloc_pages_slowpath {
>         /* ..... */
> retry:
>         /* ac->nodemask = 0x1, ac->preferred->zone->nid = 1 */
>         if (alloc_flags & ALLOC_KSWAPD)
>                 wake_all_kswapds(order, gfp_mask, ac);
>         /* cpu 1:
>         cpuset_write_resmask
>             update_nodemask
>                 update_nodemasks_hier
>                     update_tasks_nodemask
>                         mpol_rebind_task
>                          mpol_rebind_policy
>                           mpol_rebind_nodemask
> 		// mempolicy->nodes has been modified,
> 		// which ac->nodemask point to
> 
>         */
>         /* ac->nodemask = 0x3, ac->preferred->zone->nid = 1 */
>         if (should_reclaim_retry(gfp_mask, order, ac, alloc_flags,
>                                  did_some_progress > 0, &no_progress_loops))
>                 goto retry;
> }
> 
> Simultaneously starting multiple cpuset01 from LTP can quickly
> reproduce this issue on a multi node server when the maximum
> memory pressure is reached and the swap is enabled
> 
> Signed-off-by: Tianyang Zhang <zhangtianyang@loongson.cn>
> ---

What commit does it fix and should it be backported to -stable?

There's a new 'MEMORY MANAGEMENT - PAGE ALLOCATOR' entry (only in
Andrew's mm.git repository now).

Let's Cc the page allocator folks here!

-- 
Cheers,
Harry / Hyeonggon

>  mm/page_alloc.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index fd6b865cb1ab..1e82f5214a42 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -4530,6 +4530,14 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
>  	}
>  
>  retry:
> +	/*
> +	 * Deal with possible cpuset update races or zonelist updates to avoid
> +	 * infinite retries.
> +	 */
> +	if (check_retry_cpuset(cpuset_mems_cookie, ac) ||
> +	    check_retry_zonelist(zonelist_iter_cookie))
> +		goto restart;
> +
>  	/* Ensure kswapd doesn't accidentally go to sleep as long as we loop */
>  	if (alloc_flags & ALLOC_KSWAPD)
>  		wake_all_kswapds(order, gfp_mask, ac);
> -- 
> 2.20.1
> 
>