sched/psi: Fix psi_seq initialization

[ Upstream commit 99b773d ]

With the seqcount moved out of the group into a global psi_seq,
re-initializing the seqcount on group creation is causing seqcount
corruption.

Fixes: 570c8ef ("sched/psi: Optimize psi_group_change() cpu_clock() usage")
Reported-by: Chris Mason <clm@meta.com>
Suggested-by: Beata Michalska <beata.michalska@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

Author: Peter Zijlstra

kernel/sched/psi.c

@@ -172,7 +172,7 @@ struct psi_group psi_system = {
 	.pcpu = &system_group_pcpu,
 };
 
-static DEFINE_PER_CPU(seqcount_t, psi_seq);
+static DEFINE_PER_CPU(seqcount_t, psi_seq) = SEQCNT_ZERO(psi_seq);
 
 static inline void psi_write_begin(int cpu)
 {
@@ -200,11 +200,7 @@ static void poll_timer_fn(struct timer_list *t);
 
 static void group_init(struct psi_group *group)
 {
-	int cpu;
-
 	group->enabled = true;
-	for_each_possible_cpu(cpu)
-		seqcount_init(per_cpu_ptr(&psi_seq, cpu));
 	group->avg_last_update = sched_clock();
 	group->avg_next_update = group->avg_last_update + psi_period;
 	mutex_init(&group->avgs_lock);