[PATCH 3.19.y-ckt 173/251] clocksource: exynos_mct: Avoid blocking calls in the cpu hotplug notifier

[k.kozlowski@samsung.com (Krzysztof Kozlowski)]

2015-07-16 17:14 GMT+09:00 Duan Andy <fugang.duan@freescale.com>:
> From: Krzysztof Kozlowski <k.kozlowski@samsung.com> Sent: Thursday, July 16, 2015 2:56 PM
>> To: Duan Fugang-B38611
>> Cc: Kamal Mostafa; linux-kernel at vger.kernel.org; stable at vger.kernel.org;
>> kernel-team at lists.ubuntu.com; daniel.lezcano at linaro.org; Damian Eppel;
>> kyungmin.park at samsung.com; kgene at kernel.org; Thomas Gleixner; linux-arm-
>> kernel at lists.infradead.org; m.szyprowski at samsung.com
>> Subject: Re: [PATCH 3.19.y-ckt 173/251] clocksource: exynos_mct: Avoid
>> blocking calls in the cpu hotplug notifier
>>
>> 2015-07-16 15:37 GMT+09:00 Duan Andy <fugang.duan@freescale.com>:
>> > From: Kamal Mostafa <kamal@canonical.com> Sent: Thursday, July 16,
>> > 2015 9:08 AM
>> >> To: linux-kernel at vger.kernel.org; stable at vger.kernel.org; kernel-
>> >> team at lists.ubuntu.com
>> >> Cc: Kamal Mostafa; daniel.lezcano at linaro.org;
>> >> kyungmin.park at samsung.com; Damian Eppel; kgene at kernel.org; Thomas
>> >> Gleixner; linux-arm- kernel at lists.infradead.org;
>> >> m.szyprowski at samsung.com
>> >> Subject: [PATCH 3.19.y-ckt 173/251] clocksource: exynos_mct: Avoid
>> >> blocking calls in the cpu hotplug notifier
>> >>
>> >> 3.19.8-ckt4 -stable review patch.  If anyone has any objections,
>> >> please let me know.
>> >>
>> >> ------------------
>> >>
>> >> From: Damian Eppel <d.eppel@samsung.com>
>> >>
>> >> commit 56a94f13919c0db5958611b388e1581b4852f3c9 upstream.
>> >>
>> >> 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).
>> >>
>> >> [   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)
>> >>
>> >> Interrupts cannot be requested/freed in the CPU_STARTING/CPU_DYING
>> >> notifications which run on the hotplugged cpu with interrupts and
>> >> preemption disabled.
>> >>
>> >> To avoid the issue, request the interrupts for all possible cpus in
>> >> the boot code. The interrupts are marked NO_AUTOENABLE to avoid a
>> >> racy
>> >> request_irq/disable_irq() sequence. The flag prevents the
>> >> request_irq() code from enabling the interrupt immediately.
>> >>
>> >> The interrupt is then enabled in the CPU_STARTING notifier of the
>> >> hotplugged cpu and again disabled with disable_irq_nosync() in the
>> >> CPU_DYING notifier.
>> >>
>> >> [ tglx: Massaged changelog to match the patch ]
>> >>
>> >> Fixes: 7114cd749a12 ("clocksource: exynos_mct: use (request/free)_irq
>> >> calls for local timer registration")
>> >> Reported-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
>> >> Reviewed-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
>> >> Tested-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
>> >> Tested-by: Marcin Jabrzyk <m.jabrzyk@samsung.com>
>> >> Signed-off-by: Damian Eppel <d.eppel@samsung.com>
>> >> Cc: m.szyprowski at samsung.com
>> >> Cc: kyungmin.park at samsung.com
>> >> Cc: daniel.lezcano at linaro.org
>> >> Cc: kgene at kernel.org
>> >> Cc: linux-arm-kernel at lists.infradead.org
>> >> Link: http://lkml.kernel.org/r/1435324984-7328-1-git-send-email-
>> >> d.eppel at samsung.com
>> >> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
>> >> Signed-off-by: Kamal Mostafa <kamal@canonical.com>
>> >> ---
>> >>  drivers/clocksource/exynos_mct.c | 43
>> >> ++++++++++++++++++++++++++++------
>> >> ------
>> >>  1 file changed, 30 insertions(+), 13 deletions(-)
>> >>
>> >> diff --git a/drivers/clocksource/exynos_mct.c
>> >> b/drivers/clocksource/exynos_mct.c
>> >> index 83564c9..c844616 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);
>> >
>> > In here, why not use enable_percpu_irq(evt->irq) ?
>> >
>> >>       }
>> >> @@ -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]);
>> >
>> > In here, why not use disable_percpu_irq(evt->irq) ?
>>
>> You know this is just a semi-automatic stable backport and this was
>> already merged to mainline?
>>
>> Best regards,
>> Krzysztof
>
> Yes, I know. Do you know the reason why not enable other cpus irq ?
> I want to confirm whether it is right after below change ?
> enable_percpu_irq(mct_irqs[MCT_L0_IRQ], 0); -> enable_percpu_irq(evt->irq, 0);
> disable_percpu_irq(mct_irqs[MCT_L0_IRQ]) -> disable_percpu_irq(evt->irq)

This is a backport so are there any objections about this patch? Do
you think the patch is invalid so it should not be backported to
stable?

Best regards,
Krzysztof