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Date:   Tue, 21 Aug 2018 20:38:39 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Mark Rutland <mark.rutland@....com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: WARNING: CPU: 0 PID: 14 at kernel/kthread.c:501 kthread_park+0x44/0xa4
 (was: Re: kthread: Simplify kthread_park() completion)

Hoi Peter,

On Tue, Aug 14, 2018 at 12:00 AM Linux Kernel Mailing List
<linux-kernel@...r.kernel.org> wrote:
> Web:        https://git.kernel.org/torvalds/c/f83ee19be4272564ad592ef90145db7295229490
> Commit:     f83ee19be4272564ad592ef90145db7295229490
> Parent:     167a88677b05d6a810f23b871cfb2b5db1808e60
> Refname:    refs/heads/master
> Author:     Peter Zijlstra <peterz@...radead.org>
> AuthorDate: Thu Jun 7 10:55:56 2018 +0200
> Committer:  Ingo Molnar <mingo@...nel.org>
> CommitDate: Tue Jul 3 09:20:44 2018 +0200
>
>     kthread: Simplify kthread_park() completion
>
>     Oleg explains the reason we could hit park+park is that
>     smpboot_update_cpumask_percpu_thread()'s
>
>       for_each_cpu_and(cpu, &tmp, cpu_online_mask)
>             smpboot_park_kthread();
>
>     turns into:
>
>       for ((cpu) = 0; (cpu) < 1; (cpu)++, (void)mask, (void)and)
>             smpboot_park_kthread();
>
>     on UP, ignoring the mask. But since we just completely removed that
>     function, this is no longer relevant.
>
>     So revert commit:
>
>       b1f5b378e126 ("kthread: Allow kthread_park() on a parked kthread")
>
>     Suggested-by: Oleg Nesterov <oleg@...hat.com>
>     Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
>     Cc: Linus Torvalds <torvalds@...ux-foundation.org>
>     Cc: Peter Zijlstra <peterz@...radead.org>
>     Cc: Thomas Gleixner <tglx@...utronix.de>
>     Cc: linux-kernel@...r.kernel.org
>     Signed-off-by: Ingo Molnar <mingo@...nel.org>
> ---
>  kernel/kthread.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/kthread.c b/kernel/kthread.c
> index 750cb8082694..11b591ee51ab 100644
> --- a/kernel/kthread.c
> +++ b/kernel/kthread.c
> @@ -190,7 +190,7 @@ static void __kthread_parkme(struct kthread *self)
>                 if (!test_bit(KTHREAD_SHOULD_PARK, &self->flags))
>                         break;
>
> -               complete_all(&self->parked);
> +               complete(&self->parked);
>                 schedule();
>         }
>         __set_current_state(TASK_RUNNING);
> @@ -465,7 +465,6 @@ void kthread_unpark(struct task_struct *k)
>         if (test_bit(KTHREAD_IS_PER_CPU, &kthread->flags))
>                 __kthread_bind(k, kthread->cpu, TASK_PARKED);
>
> -       reinit_completion(&kthread->parked);
>         clear_bit(KTHREAD_SHOULD_PARK, &kthread->flags);
>         /*
>          * __kthread_parkme() will either see !SHOULD_PARK or get the wakeup.
> @@ -493,6 +492,9 @@ int kthread_park(struct task_struct *k)
>         if (WARN_ON(k->flags & PF_EXITING))
>                 return -ENOSYS;
>
> +       if (WARN_ON_ONCE(test_bit(KTHREAD_SHOULD_PARK, &kthread->flags)))
> +               return -EBUSY;
> +
>         set_bit(KTHREAD_SHOULD_PARK, &kthread->flags);
>         if (k != current) {
>                 wake_up_process(k);

The above WARN_ON_ONCE() triggers during psci_checker operation when booting
on R-Car Gen3 (arm64) SoCs where a trusted OS is resident on CPU0.

Reverting the commit fixes the issue.

Dmesg before/after on R-Car H3 ES2.0:

 psci: probing for conduit method from DT.
 psci: PSCIv1.0 detected in firmware.
 psci: Using standard PSCI v0.2 function IDs
 psci: Trusted OS resident on physical CPU 0x0
 psci: SMC Calling Convention v1.0
 ...
 psci_checker: Trying to turn off and on again group 0 (CPUs 0-3)
+WARNING: CPU: 0 PID: 14 at kernel/kthread.c:501 kthread_park+0x44/0xa4
+Modules linked in:
+CPU: 0 PID: 14 Comm: cpuhp/0 Not tainted
4.18.0-salvator-x-00407-gbc763e81b483a4e3 #170
+Hardware name: Renesas Salvator-X 2nd version board based on r8a7795
ES2.0+ (DT)
+pstate: 80400005 (Nzcv daif +PAN -UAO)
+pc : kthread_park+0x44/0xa4
+lr : smpboot_park_threads+0x88/0x94
+sp : ffffff8009dcbca0
+x29: ffffff8009dcbca0 x28: ffffff80081156cc
+x27: ffffff800900e000 x26: 00000046f7027000
+x25: ffffff8008e9cfc0 x24: ffffffc6ffec3fc0
+x23: ffffff80090305b8 x22: 0000000000000000
+x21: ffffffc6fb8ab200 x20: 0000000000000001
+x19: ffffff80090269e8 x18: ffffffc6fb897348
+x17: 0000000000000000 x16: 0000000000000000
+x15: 0000000000000400 x14: 0000000000000400
+x13: 0000000000000400 x12: 0000000000000001
+x11: 0000000000000400 x10: 0000000000000400
+x9 : 0000000000000125 x8 : 0000000000000000
+x7 : ffffff80081156f8 x6 : 0000000000000001
+x5 : 0000000000000000 x4 : ffffff8009804b40
+x3 : 000000007cbd3c4e x2 : 38716e04a5aa3600
+x1 : 0000000004208040 x0 : ffffffc6fb95c240
+Call trace:
+ kthread_park+0x44/0xa4
+ smpboot_park_threads+0x88/0x94
+ cpuhp_invoke_callback+0x230/0xcfc
+ cpuhp_thread_fun+0xb8/0x1d8
+ smpboot_thread_fn+0x228/0x244
+ kthread+0x124/0x134
+ ret_from_fork+0x10/0x18
+irq event stamp: 3390
+hardirqs last  enabled at (3389): [<ffffff800818729c>]
generic_exec_single+0x80/0x11c
+hardirqs last disabled at (3390): [<ffffff80080818cc>]
do_debug_exception+0x5c/0x17c
+softirqs last  enabled at (1810): [<ffffff8008081da8>] __do_softirq+0x160/0x4ec
+softirqs last disabled at (1795): [<ffffff80080ed460>] irq_exit+0xa4/0x100
+---[ end trace 518ee2fb840813cb ]---
 CPU1: shutdown
 psci: CPU1 killed.
-NOHZ: local_softirq_pending 51
+NOHZ: local_softirq_pending 55
 CPU2: shutdown
 psci: CPU2 killed.
 NOHZ: local_softirq_pending 51
 CPU3: shutdown
 psci: CPU3 killed.
 Detected PIPT I-cache on CPU1
 CPU1: Booted secondary processor 0x0000000001 [0x411fd073]
 Detected PIPT I-cache on CPU2
 CPU2: Booted secondary processor 0x0000000002 [0x411fd073]
 Detected PIPT I-cache on CPU3
 CPU3: Booted secondary processor 0x0000000003 [0x411fd073]

The issue can also be seen on R-Car M3-W and M3-N.
It does not happen on R-Car H3 ES1.0 with an older firmware version, where
no trusted OS is running on CPU0 ("psci: Trusted OS migration not required").

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

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