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Message-Id: <20250704135620.685752-1-yu.c.chen@intel.com>
Date: Fri, 4 Jul 2025 21:56:20 +0800
From: Chen Yu <yu.c.chen@...el.com>
To: Ingo Molnar <mingo@...hat.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Peter Zijlstra <peterz@...radead.org>
Cc: Chen Yu <yu.c.chen@...el.com>,
Jirka Hladky <jhladky@...hat.com>,
Srikanth Aithal <Srikanth.Aithal@....com>,
Suneeth D <Suneeth.D@....com>,
Libo Chen <libo.chen@...cle.com>,
Michal Hocko <mhocko@...e.com>,
linux-kernel@...r.kernel.org
Subject: [PATCH] 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.
Fixes: ad6b26b6a0a7 ("sched/numa: add statistics of numa balance task")
Reported-by: Jirka Hladky <jhladky@...hat.com>
Closes: https://lore.kernel.org/all/CAE4VaGBLJxpd=NeRJXpSCuw=REhC5LWJpC29kDy-Zh2ZDyzQZA@mail.gmail.com/
Reported-by: Srikanth Aithal <Srikanth.Aithal@....com>
Reported-by: Suneeth D <Suneeth.D@....com>
Signed-off-by: Chen Yu <yu.c.chen@...el.com>
---
Documentation/admin-guide/cgroup-v2.rst | 6 ------
include/linux/sched.h | 4 ----
include/linux/vm_event_item.h | 2 --
kernel/sched/core.c | 9 ++-------
kernel/sched/debug.c | 4 ----
mm/memcontrol.c | 2 --
mm/vmstat.c | 2 --
7 files changed, 2 insertions(+), 27 deletions(-)
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.
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 4f78a64beb52..aa9c5be7a632 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -548,10 +548,6 @@ struct sched_statistics {
u64 nr_failed_migrations_running;
u64 nr_failed_migrations_hot;
u64 nr_forced_migrations;
-#ifdef CONFIG_NUMA_BALANCING
- u64 numa_task_migrated;
- u64 numa_task_swapped;
-#endif
u64 nr_wakeups;
u64 nr_wakeups_sync;
diff --git a/include/linux/vm_event_item.h b/include/linux/vm_event_item.h
index 91a3ce9a2687..9e15a088ba38 100644
--- a/include/linux/vm_event_item.h
+++ b/include/linux/vm_event_item.h
@@ -66,8 +66,6 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
NUMA_HINT_FAULTS,
NUMA_HINT_FAULTS_LOCAL,
NUMA_PAGE_MIGRATE,
- NUMA_TASK_MIGRATE,
- NUMA_TASK_SWAP,
#endif
#ifdef CONFIG_MIGRATION
PGMIGRATE_SUCCESS, PGMIGRATE_FAIL,
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 8988d38d46a3..ca0be74e865b 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3362,10 +3362,6 @@ void set_task_cpu(struct task_struct *p, unsigned int new_cpu)
#ifdef CONFIG_NUMA_BALANCING
static void __migrate_swap_task(struct task_struct *p, int cpu)
{
- __schedstat_inc(p->stats.numa_task_swapped);
- count_vm_numa_event(NUMA_TASK_SWAP);
- count_memcg_event_mm(p->mm, NUMA_TASK_SWAP);
-
if (task_on_rq_queued(p)) {
struct rq *src_rq, *dst_rq;
struct rq_flags srf, drf;
@@ -7934,9 +7930,8 @@ int migrate_task_to(struct task_struct *p, int target_cpu)
if (!cpumask_test_cpu(target_cpu, p->cpus_ptr))
return -EINVAL;
- __schedstat_inc(p->stats.numa_task_migrated);
- count_vm_numa_event(NUMA_TASK_MIGRATE);
- count_memcg_event_mm(p->mm, NUMA_TASK_MIGRATE);
+ /* TODO: This is not properly updating schedstats */
+
trace_sched_move_numa(p, curr_cpu, target_cpu);
return stop_one_cpu(curr_cpu, migration_cpu_stop, &arg);
}
diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index 9d71baf08075..557246880a7e 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -1210,10 +1210,6 @@ void proc_sched_show_task(struct task_struct *p, struct pid_namespace *ns,
P_SCHEDSTAT(nr_failed_migrations_running);
P_SCHEDSTAT(nr_failed_migrations_hot);
P_SCHEDSTAT(nr_forced_migrations);
-#ifdef CONFIG_NUMA_BALANCING
- P_SCHEDSTAT(numa_task_migrated);
- P_SCHEDSTAT(numa_task_swapped);
-#endif
P_SCHEDSTAT(nr_wakeups);
P_SCHEDSTAT(nr_wakeups_sync);
P_SCHEDSTAT(nr_wakeups_migrate);
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 902da8a9c643..70fdeda1120b 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -474,8 +474,6 @@ static const unsigned int memcg_vm_event_stat[] = {
NUMA_PAGE_MIGRATE,
NUMA_PTE_UPDATES,
NUMA_HINT_FAULTS,
- NUMA_TASK_MIGRATE,
- NUMA_TASK_SWAP,
#endif
};
diff --git a/mm/vmstat.c b/mm/vmstat.c
index 429ae5339bfe..a78d70ddeacd 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1346,8 +1346,6 @@ const char * const vmstat_text[] = {
"numa_hint_faults",
"numa_hint_faults_local",
"numa_pages_migrated",
- "numa_task_migrated",
- "numa_task_swapped",
#endif
#ifdef CONFIG_MIGRATION
"pgmigrate_success",
--
2.25.1
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