Re: [PATCH] clocksource: exynos_mct: fix for sleeping in atomic ctx handling cpu hotplug notif.

[Krzysztof KozÅowski]

2015-01-30 15:21 GMT+01:00 Damian Eppel <d.eppel@xxxxxxxxxxx>:
> This is to fix an issue of sleeping in atomic context when processing
> hotplug notifications in Exynos MCT(Multi-Core Timer).
> The issue was reproducible on Exynos 3250 (Rinato board) and Exynos 5420
> (Arndale Octa board).
>
> Whilst testing cpu hotplug events on kernel configured with DEBUG_PREEMPT
> and DEBUG_ATOMIC_SLEEP we get following BUG message, caused by calling
> request_irq() and free_irq() in the context of hotplug notification
> (which is in this case atomic context).
>
> root@target:~# echo 0 > /sys/devices/system/cpu/cpu1/online
>
> [   25.157867] IRQ18 no longer affine to CPU1
> ...
> [   25.158445] CPU1: shutdown
>
> root@target:~# echo 1 > /sys/devices/system/cpu/cpu1/online
>
> [   40.785859] CPU1: Software reset
> [   40.786660] BUG: sleeping function called from invalid context at mm/slub.c:1241
> [   40.786668] in_atomic(): 1, irqs_disabled(): 128, pid: 0, name: swapper/1
> [   40.786678] Preemption disabled at:[<  (null)>]   (null)
> [   40.786681]
> [   40.786692] CPU: 1 PID: 0 Comm: swapper/1 Not tainted 3.19.0-rc4-00024-g7dca860 #36
> [   40.786698] Hardware name: SAMSUNG EXYNOS (Flattened Device Tree)
> [   40.786728] [<c0014a00>] (unwind_backtrace) from [<c0011980>] (show_stack+0x10/0x14)
> [   40.786747] [<c0011980>] (show_stack) from [<c0449ba0>] (dump_stack+0x70/0xbc)
> [   40.786767] [<c0449ba0>] (dump_stack) from [<c00c6124>] (kmem_cache_alloc+0xd8/0x170)
> [   40.786785] [<c00c6124>] (kmem_cache_alloc) from [<c005d6f8>] (request_threaded_irq+0x64/0x128)
> [   40.786804] [<c005d6f8>] (request_threaded_irq) from [<c0350b8c>] (exynos4_local_timer_setup+0xc0/0x13c)
> [   40.786820] [<c0350b8c>] (exynos4_local_timer_setup) from [<c0350ca8>] (exynos4_mct_cpu_notify+0x30/0xa8)
> [   40.786838] [<c0350ca8>] (exynos4_mct_cpu_notify) from [<c003b330>] (notifier_call_chain+0x44/0x84)
> [   40.786857] [<c003b330>] (notifier_call_chain) from [<c0022fd4>] (__cpu_notify+0x28/0x44)
> [   40.786873] [<c0022fd4>] (__cpu_notify) from [<c0013714>] (secondary_start_kernel+0xec/0x150)
> [   40.786886] [<c0013714>] (secondary_start_kernel) from [<40008764>] (0x40008764)
>
> Solution:
> Clockevent irqs cannot be requested/freed every time cpu is
> hot-plugged/unplugged as CPU_STARTING/CPU_DYING notifications
> that signals hotplug or unplug events are sent with both preemption
> and local interrupts disabled. Since request_irq() may sleep it is
> moved to the initialization stage and performed for all possible
> cpus prior putting them online. Then, in the case of hotplug event
> the irq asociated with the given cpu will simply be enabled.
> Similarly on cpu unplug event the interrupt is not freed but just
> disabled.
>
> Note that after successful request_irq() call for a clockevent device
> associated to given cpu the requested irq is disabled (via disable_irq()).
> That is to make things symmetric as we expect hotplug event as a next
> thing (which will enable irq again). This should not pose any problems
> because at the time of requesting irq the clockevent device is not
> fully initialized yet, therefore should not produce interrupts at that point.
>
> For disabling an irq at cpu unplug notification disable_irq_nosync() is
> chosen which is a non-blocking function. This again shouldn't be a problem as
> prior sending CPU_DYING notification interrupts are migrated away
> from the cpu.
>
> Fixes: 7114cd749a12 ("clocksource: exynos_mct: use (request/free)_irq calls for local timer registration")
> Signed-off-by: Damian Eppel <d.eppel@xxxxxxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx>
> Reported-by: Krzysztof Kozlowski <k.kozlowski@xxxxxxxxxxx>
> ---
>  drivers/clocksource/exynos_mct.c | 45 ++++++++++++++++++++++++++++------------
>  1 file changed, 32 insertions(+), 13 deletions(-)

Hi,

Look fine from my point of view.
Reviewed-by: Krzysztof Kozlowski <k.kozlowski@xxxxxxxxxxx>

Tested on Arndale Octa Board. Fixes the sleep-in-atomic.
Tested-by: Krzysztof Kozlowski <k.kozlowski@xxxxxxxxxxx>

Best regards,
Krzysztof

>
> diff --git a/drivers/clocksource/exynos_mct.c b/drivers/clocksource/exynos_mct.c
> index 83564c9..9beca58 100644
> --- a/drivers/clocksource/exynos_mct.c
> +++ b/drivers/clocksource/exynos_mct.c
> @@ -466,15 +466,12 @@ static int exynos4_local_timer_setup(struct clock_event_device *evt)
>         exynos4_mct_write(TICK_BASE_CNT, mevt->base + MCT_L_TCNTB_OFFSET);
>
>         if (mct_int_type == MCT_INT_SPI) {
> -               evt->irq = mct_irqs[MCT_L0_IRQ + cpu];
> -               if (request_irq(evt->irq, exynos4_mct_tick_isr,
> -                               IRQF_TIMER | IRQF_NOBALANCING,
> -                               evt->name, mevt)) {
> -                       pr_err("exynos-mct: cannot register IRQ %d\n",
> -                               evt->irq);
> +
> +               if (evt->irq == -1)
>                         return -EIO;
> -               }
> -               irq_force_affinity(mct_irqs[MCT_L0_IRQ + cpu], cpumask_of(cpu));
> +
> +               irq_force_affinity(evt->irq, cpumask_of(cpu));
> +               enable_irq(evt->irq);
>         } else {
>                 enable_percpu_irq(mct_irqs[MCT_L0_IRQ], 0);
>         }
> @@ -487,10 +484,12 @@ static int exynos4_local_timer_setup(struct clock_event_device *evt)
>  static void exynos4_local_timer_stop(struct clock_event_device *evt)
>  {
>         evt->set_mode(CLOCK_EVT_MODE_UNUSED, evt);
> -       if (mct_int_type == MCT_INT_SPI)
> -               free_irq(evt->irq, this_cpu_ptr(&percpu_mct_tick));
> -       else
> +       if (mct_int_type == MCT_INT_SPI) {
> +               if (evt->irq != -1)
> +                       disable_irq_nosync(evt->irq);
> +       } else {
>                 disable_percpu_irq(mct_irqs[MCT_L0_IRQ]);
> +       }
>  }
>
>  static int exynos4_mct_cpu_notify(struct notifier_block *self,
> @@ -522,7 +521,7 @@ static struct notifier_block exynos4_mct_cpu_nb = {
>
>  static void __init exynos4_timer_resources(struct device_node *np, void __iomem *base)
>  {
> -       int err;
> +       int err, cpu;
>         struct mct_clock_event_device *mevt = this_cpu_ptr(&percpu_mct_tick);
>         struct clk *mct_clk, *tick_clk;
>
> @@ -549,7 +548,27 @@ static void __init exynos4_timer_resources(struct device_node *np, void __iomem
>                 WARN(err, "MCT: can't request IRQ %d (%d)\n",
>                      mct_irqs[MCT_L0_IRQ], err);
>         } else {
> -               irq_set_affinity(mct_irqs[MCT_L0_IRQ], cpumask_of(0));
> +               for_each_possible_cpu(cpu) {
> +                       int mct_irq = mct_irqs[MCT_L0_IRQ + cpu];
> +                       struct mct_clock_event_device *pcpu_mevt =
> +                               per_cpu_ptr(&percpu_mct_tick, cpu);
> +
> +                       pcpu_mevt->evt.irq = -1;
> +
> +                       if (request_irq(mct_irq,
> +                                       exynos4_mct_tick_isr,
> +                                       IRQF_TIMER | IRQF_NOBALANCING,
> +                                       pcpu_mevt->name, pcpu_mevt)) {
> +                               pr_err("exynos-mct: cannot register IRQ (cpu%d)\n",
> +                                                                       cpu);
> +
> +                               continue;
> +                       }
> +                       pcpu_mevt->evt.irq = mct_irq;
> +                       irq_force_affinity(mct_irq, cpumask_of(cpu));
> +
> +                       disable_irq(mct_irq);
> +               }
>         }
>
>         err = register_cpu_notifier(&exynos4_mct_cpu_nb);
> --
> 1.9.1
>
>
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