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

[Tianyang Zhang <zhangtianyang@loongson.cn>]

Hi.

在 2025/4/21 下午6:00, Harry Yoo 写道:
> 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!

We first identified this issue in 6.6.52-stable , and through root cause 
analysis,

it appears the problem may have existed for a significant period.

However It is recommended that the fix should be backported to at least 
Linux kernel versions after 6.6-stable