[PATCH v2] sched/pelt: Fix truncation of the PELT period count

[Hui Su]

accumulate_sum() computes the number of elapsed PELT periods in a
u64 but returns u32. When the count is a multiple of 2^32, it is
truncated to zero even though the PELT sums have been updated.

The caller interprets zero as no period boundary crossed and skips
recomputing the averages, leaving *_avg stale relative to *_sum.

Return the period count as u64 so the caller can test it without
truncation.

Fixes: a481db34b9be ("sched/fair: Optimize ___update_sched_avg()")
Reviewed-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
Reviewed-by: Kayra Cizmeci <kayracizmeci@xxxxxxxxx>
Signed-off-by: Hui Su <sh_def@xxxxxxx>
---
Changes in v2:
- Return the PELT period count as u64.
- Add the Fixes tag and Kayra Cizmeci's Reviewed-by.

v1: https://lore.kernel.org/lkml/20261022034930.225042-1-sh_def@xxxxxxx/

 kernel/sched/pelt.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/pelt.c b/kernel/sched/pelt.c
index 779eb58a4261..d10d57b6b8ec 100644
--- a/kernel/sched/pelt.c
+++ b/kernel/sched/pelt.c
@@ -99,7 +99,7 @@ static u32 __accumulate_pelt_segments(u64 periods, u32 d1, u32 d3)
  *      d1 y^p + 1024 \Sum y^n + d3 y^0		(Step 2)
  *                     n=1
  */
-static __always_inline u32
+static __always_inline u64
 accumulate_sum(u64 delta, struct sched_avg *sa,
 	       unsigned long load, unsigned long runnable, int running)
 {

base-commit: a804c5742bff224d4cb4d25dd383554d598be32b
-- 
2.55.0