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

[Andrew Morton <akpm@linux-foundation.org>]

On Tue, 13 May 2025 09:26:53 -0700 Suren Baghdasaryan <surenb@google.com> wrote:

> > > > This has been in mm-hotfixes-unstable for six days.  Hopefully we'll
> > > > see some review activity soon (please).
> > >
> > > I reviewed and provided my feedback but saw neither a reply nor a
> > > respin with proposed changes.
> >
> > OK, thanks.  Do you have time to put together a modified version of this?
> 
> I think the code is fine as is. Would be good to add Fixes: tag but it
> will require some investigation to find the appropriate patch to
> reference here.

Below is what is in mm-hotfixes.  It doesn't actually have any
acked-by's or reviewed-by's.

So... final call for review, please.


From: Tianyang Zhang <zhangtianyang@loongson.cn>
Subject: mm/page_alloc.c: avoid infinite retries caused by cpuset race
Date: Wed, 16 Apr 2025 16:24:05 +0800

__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

Link: https://lkml.kernel.org/r/20250416082405.20988-1-zhangtianyang@loongson.cn
Fixes: 902b62810a57 ("mm, page_alloc: fix more premature OOM due to race with cpuset update").
Signed-off-by: Tianyang Zhang <zhangtianyang@loongson.cn>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Brendan Jackman <jackmanb@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Zi Yan <ziy@nvidia.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/page_alloc.c |    8 ++++++++
 1 file changed, 8 insertions(+)

--- a/mm/page_alloc.c~mm-page_allocc-avoid-infinite-retries-caused-by-cpuset-race
+++ a/mm/page_alloc.c
@@ -4562,6 +4562,14 @@ restart:
 	}
 
 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);
_