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>> for_each_possible_cpu(cpu) >> - seqcount_init(&per_cpu_ptr(group->pcpu, cpu)->seq); >> + 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); > > I'm not sure if someone mentioned this already, but testing the > series I got a bunch of softlockups in get_recent_times() > that randomly jumped from CPU to CPU. Ayush, Srikanth, and I ran into this yesterday when testing different trees (next, queue:sched/core) with similar signatures: watchdog: BUG: soft lockup - CPU#0 stuck for 21s! [kworker/0:3:2140] Modules linked in: ... CPU: 0 UID: 0 PID: 2140 Comm: kworker/0:3 Not tainted 6.16.0-rc1-test+ #20 PREEMPT(voluntary) Hardware name: Dell Inc. PowerEdge R6525/024PW1, BIOS 2.7.3 03/30/2022 Workqueue: events psi_avgs_work RIP: 0010:collect_percpu_times+0x3a0/0x670 Code: 65 48 2b 05 4a 79 d2 02 0f 85 dc 02 00 00 48 8d 65 d8 5b 41 5c 41 5d 41 5e 41 5f 5d e9 34 ba d2 ff f3 90 49 81 ff ff 1f 00 00 <0f> 86 73 fd ff ff 4c 89 fe 48 c7 c7 80 9d 29 bb e8 cb 92 73 00 e9 RSP: 0018:ffffcda753383d10 EFLAGS: 00000297 RAX: ffff8be86fadcd40 RBX: ffffeda7308d4580 RCX: 000000000000006b RDX: 000000000000002b RSI: 0000000000000100 RDI: ffffffffbab3f400 RBP: ffffcda753383e30 R08: 000000000000006b R09: 0000000000000000 R10: 0000008cca6be372 R11: 0000000000000006 R12: 000000000000006b R13: ffffeda7308d4594 R14: 00000000000037e5 R15: 000000000000006b FS: 0000000000000000(0000) GS:ffff8ba8c1118000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 000055b3cf990c3c CR3: 000000807dc40006 CR4: 0000000000f70ef0 PKRU: 55555554 Call Trace: ? srso_alias_return_thunk+0x5/0xfbef5 ? psi_group_change+0x1ff/0x460 ? add_timer_on+0x10a/0x160 psi_avgs_work+0x4c/0xd0 ? queue_delayed_work_on+0x6d/0x80 process_one_work+0x193/0x3c0 worker_thread+0x29d/0x3c0 ? __pfx_worker_thread+0x10/0x10 kthread+0xff/0x210 ? __pfx_kthread+0x10/0x10 ? __pfx_kthread+0x10/0x10 ret_from_fork+0x171/0x1a0 ? __pfx_kthread+0x10/0x10 ret_from_fork_asm+0x1a/0x30 I was able to reproduce this reliably running 100 copies of an infinite loop doing - cgroup create, move a task, move task back to root, remove cgroup - alongside hackbench running in a seperate cgroup and I hit this in ~5-10min. I have been running the same test with your fix and haven't run into this for over 30min now. Feel free to add: Reviewed-and-tested-by: K Prateek Nayak > > This fixed it for me, but reading it now I'm wondering > if we want to seqcount_init() unconditionally even when PSI > is off. Looking at "psi_enable", it can only be toggled via the kernel parameter "psi=" and I don't see anything that does a "static_branch_disable(&psi_disabled)" at runtime so I think your fix should be good. > > diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c > index 2024c1d36402d..979a447bc281f 100644 > --- a/kernel/sched/psi.c > +++ b/kernel/sched/psi.c > @@ -207,8 +207,6 @@ static void group_init(struct psi_group *group) > int cpu; "cpu" variable can be removed too from group_init() now. > > 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); > @@ -231,6 +229,7 @@ static void group_init(struct psi_group *group) > > void __init psi_init(void) > { > + int cpu; nit. newline after declaration. > if (!psi_enable) { > static_branch_enable(&psi_disabled); > static_branch_disable(&psi_cgroups_enabled); > @@ -241,6 +240,8 @@ void __init psi_init(void) > static_branch_disable(&psi_cgroups_enabled); > > psi_period = jiffies_to_nsecs(PSI_FREQ); > + for_each_possible_cpu(cpu) > + seqcount_init(per_cpu_ptr(&psi_seq, cpu)); > group_init(&psi_system); > } > > -- Thanks and Regards, Prateek