This reverts commit ad6b26b6a0.
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: ad6b26b6a0 ("sched/numa: add statistics of numa balance task")
Signed-off-by: Chen Yu <yu.c.chen@intel.com>
Reported-by: Jirka Hladky <jhladky@redhat.com>
Closes: https://lore.kernel.org/all/CAE4VaGBLJxpd=NeRJXpSCuw=REhC5LWJpC29kDy-Zh2ZDyzQZA@mail.gmail.com/
Reported-by: Srikanth Aithal <Srikanth.Aithal@amd.com>
Reported-by: Suneeth D <Suneeth.D@amd.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Hladky <jhladky@redhat.com>
Cc: Libo Chen <libo.chen@oracle.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
db6cc3f4ac