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

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Message-ID: <75a7258b-224c-c4f2-47a9-fda3775d268c@loongson.cn>
Date: Thu, 15 May 2025 11:19:20 +0800
From: Tianyang Zhang <zhangtianyang@...ngson.cn>
To: Vlastimil Babka <vbabka@...e.cz>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Suren Baghdasaryan <surenb@...gle.com>
Cc: Harry Yoo <harry.yoo@...cle.com>, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org, Michal Hocko <mhocko@...e.com>,
 Brendan Jackman <jackmanb@...gle.com>, Johannes Weiner <hannes@...xchg.org>,
 Zi Yan <ziy@...dia.com>
Subject: Re: [PATCH] mm/page_alloc.c: Avoid infinite retries caused by cpuset
 race

Hi,

在 2025/5/14 下午3:34, Vlastimil Babka 写道:
> On 5/13/25 21:16, Andrew Morton wrote:
>> On Tue, 13 May 2025 09:26:53 -0700 Suren Baghdasaryan <surenb@...gle.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@...ngson.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").
> After the discussion in this thread, Suren retracted this Fixes: suggestion.
> I think it actually goes back to this one which introduced the
> preferred_zoneref caching.
>
> Fixes: c33d6c06f60f ("mm, page_alloc: avoid looking up the first zone in a
> zonelist twice")
Yes, the problem should be introduced by this patch, thank you
>
>> Signed-off-by: Tianyang Zhang <zhangtianyang@...ngson.cn>
>> Cc: Vlastimil Babka <vbabka@...e.cz>
>> Cc: Suren Baghdasaryan <surenb@...gle.com>
>> Cc: Michal Hocko <mhocko@...e.com>
>> Cc: Brendan Jackman <jackmanb@...gle.com>
>> Cc: Johannes Weiner <hannes@...xchg.org>
>> Cc: Zi Yan <ziy@...dia.com>
>> Cc: <stable@...r.kernel.org>
>> Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
> I would have placed the check bit further down, just above the
> should_reclaim_retry() call, but it's not that important to hold up a fix
> and can be done later.
>
> Reviewed-by: Vlastimil Babka <vbabka@...e.cz>
>
>> ---
>>
>>   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);
>> _
>>