[PATCH v3] sched/fair: Reset NUMA fault locality after scan period update

[Eric Kim]

When updating the task scan period for NUMA locality checks,
update_task_scan_period() checks whether there were no faults or failed
migration on the last scan window, at which it prolongs the scan period.

However, p->numa_faults_locality, which is used to check for migration
failure and number of faults at the previous scan window is not cleared
after changing the scan period, which unintentionally increases
numa_scan_period up to numa_scan_period_max even when there were no
migration failures or no faults at previous scan.

Fix this by jumping to the out label on early exit at this case to
ensure p->numa_faults_locality is always cleared before returning.

Reported-by: Binwon Song <qlsdnjs236@xxxxxxxxxxxxxx>
Closes: https://lore.kernel.org/all/20250404095354.311156-1-qlsdnjs236@xxxxxxxxxxxxxx/
Signed-off-by: Eric Kim <seohyun.kim@xxxxxxxxxx>
---
v3:
- Polished commit message for clarity and updated subsystem prefix to
  sched/fair.
v2:
- Share numa_faults_locality reset path with the tail of
  update_task_scan_period.(Peter zijlstra)
- Link: https://lore.kernel.org/all/OS7PR01MB139144C7E07C97B3F3B47016796D52@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/
v1:
- Link: https://lore.kernel.org/all/OS7PR01MB13914DA08AC588DE5544B03E796D62@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/

kernel/sched/fair.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index f15f5764818e..b067f6bcd941 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3469,7 +3469,7 @@ static void update_task_scan_period(struct task_struct *p,
 		p->mm->numa_next_scan = jiffies +
 			msecs_to_jiffies(p->numa_scan_period);
 
-		return;
+		goto out;
 	}
 
 	/*
@@ -3513,7 +3513,10 @@ static void update_task_scan_period(struct task_struct *p,
 
 	p->numa_scan_period = clamp(p->numa_scan_period + diff,
 			task_scan_min(p), task_scan_max(p));
-	memset(p->numa_faults_locality, 0, sizeof(p->numa_faults_locality));
+
+out:
+	memset(p->numa_faults_locality, 0,
+	       sizeof(p->numa_faults_locality));
 }
 
 /*
-- 
2.55.0