From db6cc3f4ac2e6cdc898fc9cbc8b32ae1bf56bdad Mon Sep 17 00:00:00 2001 From: Chen Yu Date: Fri, 4 Jul 2025 21:56:20 +0800 Subject: Revert "sched/numa: add statistics of numa balance task" This reverts commit ad6b26b6a0a79166b53209df2ca1cf8636296382. This commit introduces per-memcg/task NUMA balance statistics, but unfortunately it introduced a NULL pointer exception due to the following race condition: After a swap task candidate was chosen, its mm_struct pointer was set to NULL due to task exit. Later, when performing the actual task swapping, the p->mm caused the problem. CPU0 CPU1 : ... task_numa_migrate task_numa_find_cpu task_numa_compare # a normal task p is chosen env->best_task = p # p exit: exit_signals(p); p->flags |= PF_EXITING exit_mm p->mm = NULL; migrate_swap_stop __migrate_swap_task((arg->src_task, arg->dst_cpu) count_memcg_event_mm(p->mm, NUMA_TASK_SWAP)# p->mm is NULL task_lock() should be held and the PF_EXITING flag needs to be checked to prevent this from happening. After discussion, the conclusion was that adding a lock is not worthwhile for some statistics calculations. Revert the change and rely on the tracepoint for this purpose. Link: https://lkml.kernel.org/r/20250704135620.685752-1-yu.c.chen@intel.com Link: https://lkml.kernel.org/r/20250708064917.BBD13C4CEED@smtp.kernel.org Fixes: ad6b26b6a0a7 ("sched/numa: add statistics of numa balance task") Signed-off-by: Chen Yu Reported-by: Jirka Hladky Closes: https://lore.kernel.org/all/CAE4VaGBLJxpd=NeRJXpSCuw=REhC5LWJpC29kDy-Zh2ZDyzQZA@mail.gmail.com/ Reported-by: Srikanth Aithal Reported-by: Suneeth D Acked-by: Michal Hocko Cc: Borislav Petkov Cc: Ingo Molnar Cc: Jiri Hladky Cc: Libo Chen Cc: Peter Zijlstra Cc: Thomas Gleixner Signed-off-by: Andrew Morton --- Documentation/admin-guide/cgroup-v2.rst | 6 ------ 1 file changed, 6 deletions(-) (limited to 'Documentation') diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst index 0cc35a14afbe..bd98ea3175ec 100644 --- a/Documentation/admin-guide/cgroup-v2.rst +++ b/Documentation/admin-guide/cgroup-v2.rst @@ -1732,12 +1732,6 @@ The following nested keys are defined. numa_hint_faults (npn) Number of NUMA hinting faults. - numa_task_migrated (npn) - Number of task migration by NUMA balancing. - - numa_task_swapped (npn) - Number of task swap by NUMA balancing. - pgdemote_kswapd Number of pages demoted by kswapd. -- cgit v1.2.3