On Tue, Aug 21, 2018 at 9:37 PM Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> wrote:
> On Tue, Jul 31, 2018 at 6:08 PM Geert Uytterhoeven
> <geert+renesas@xxxxxxxxx> wrote:
> > SH-Mobile AG5 and R-Car H1 SoCs are based on the Cortex-A9 MPCore, which
> > includes a global timer.
> >
> > Enable the ARM global timer on these SoCs, which will be used for:
> > - the scheduler clock, improving scheduler accuracy from 10 ms to 3 or
> > 4 ns,
> > - delay loops, allowing removal of calls to shmobile_init_delay() from
> > the corresponding machine vectors.
> >
> > Note that when using an old DTB lacking the global timer, the kernel
> > will still work. However, loops-per-jiffies will no longer be preset,
> > and the delay loop will need to be calibrated during boot.
> >
> > Signed-off-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>
>
> This seems to cause random system resume issues on the venerable SH-Mobile
> AG5, ranging from plain lockups to RCU warnings:
>
> WARNING: suspicious RCU usage
> 4.18.0-kzm9g-00218-gaf4425056bd09e9e #38 Not tainted
> -----------------------------
> kernel/sched/fair.c:6231 suspicious rcu_dereference_check() usage!
>
> other info that might help us debug this:
>
>
> RCU used illegally from offline CPU!
> rcu_scheduler_active = 2, debug_locks = 1
> 3 locks held by swapper/1/0:
> #0: 6d7f5781 ((cpu_died).wait.lock){....}, at: complete+0x14/0x48
> #1: 84ce6f8e (&p->pi_lock){-.-.}, at: try_to_wake_up+0x30/0x3cc
> #2: 93591133 (rcu_read_lock){....}, at: select_task_rq_fair+0x5c/0xe8c
>
> stack backtrace:
> CPU: 1 PID: 0 Comm: swapper/1 Not tainted
> 4.18.0-kzm9g-00218-gaf4425056bd09e9e #38
> Hardware name: Generic SH73A0 (Flattened Device Tree)
> [<c010f22c>] (unwind_backtrace) from [<c010bab0>] (show_stack+0x10/0x14)
> [<c010bab0>] (show_stack) from [<c0599750>] (dump_stack+0x9c/0xd4)
> [<c0599750>] (dump_stack) from [<c01542c8>] (select_task_rq_fair+0x140/0xe8c)
> [<c01542c8>] (select_task_rq_fair) from [<c0149494>]
> (try_to_wake_up+0x210/0x3cc)
> [<c0149494>] (try_to_wake_up) from [<c016355c>] (__wake_up_common+0xcc/0x140)
> [<c016355c>] (__wake_up_common) from [<c01636a8>] (__wake_up_locked+0x14/0x1c)
> [<c01636a8>] (__wake_up_locked) from [<c016450c>] (complete+0x38/0x48)
> [<c016450c>] (complete) from [<c010d66c>] (arch_cpu_idle_dead+0x2c/0x8c)
> [<c010d66c>] (arch_cpu_idle_dead) from [<c014edec>] (do_idle+0x98/0x148)
> [<c014edec>] (do_idle) from [<c014f1fc>] (cpu_startup_entry+0x18/0x1c)
> [<c014f1fc>] (cpu_startup_entry) from [<4010246c>] (0x4010246c)
>
> Given secondary CPU startup is already quite flaky on this SoC, perhaps
> it's best to leave it alone?
Last time I saw that was on v4.19-rc7 in October.
Presumably that was fixed in the big RCU update in v4.20-rc1, so I think
it's safe to use the Global Timer on SH Mobile AG5 now.
Thoughts?
Thanks!
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
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
