[PATCH 5.10 595/798] block/blk-iocost: collect per-cpu latency stats over possible CPUs

5.10-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Tao Cui <redacted>

[ Upstream commit 4e050c5b92c1600415b2cd452583e543036f3d73 ]

ioc_lat_stat() walks ioc->pcpu_stat with for_each_online_cpu() to
compute missed-ppm and rq_wait deltas.  An offlined CPU is skipped, so
its delta is dropped from the period and its last_* watermark is not
advanced; on re-online the next collection sees a delta spanning the
whole offline interval, corrupting the latency/vrate picture.

Fixes: 7caa47151ab2 ("blkcg: implement blk-iocost")
Signed-off-by: Tao Cui <redacted>
Reviewed-by: Yu Kuai <yukuai@fygo.io>
Link: https://patch.msgid.link/20260720093726.28965-4-cui.tao@linux.dev (local)
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 block/blk-iocost.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/block/blk-iocost.c b/block/blk-iocost.c
index 6e895fa90602a..98866b3bfc275 100644
--- a/block/blk-iocost.c
+++ b/block/blk-iocost.c

@@ -1546,7 +1546,7 @@ static void ioc_lat_stat(struct ioc *ioc, u32 *missed_ppm_ar, u32 *rq_wait_pct_p
 	u64 rq_wait_ns = 0;
 	int cpu, rw;
 
-	for_each_online_cpu(cpu) {
+	for_each_possible_cpu(cpu) {
 		struct ioc_pcpu_stat *stat = per_cpu_ptr(ioc->pcpu_stat, cpu);
 		u64 this_rq_wait_ns;
 

-- 
2.53.0