linux-kernel - Re: [PATCH] irqchip: mips-gic: Avoid spuriously handling masked interrupts

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Message-ID: <6b8c8416-a02a-940c-71b0-fc9c13101740@mips.com>
Date:   Wed, 7 Feb 2018 11:11:41 +0000
From:   Matt Redfearn <matt.redfearn@...s.com>
To:     Marc Zyngier <marc.zyngier@....com>,
        Thomas Gleixner <tglx@...utronix.de>
CC:     <linux-mips@...ux-mips.org>, Ralf Baechle <ralf@...ux-mips.org>,
        "Jason Cooper" <jason@...edaemon.net>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] irqchip: mips-gic: Avoid spuriously handling masked
 interrupts

Hi Marc,

On 07/02/18 10:41, Marc Zyngier wrote:
> On 07/02/18 09:44, Matt Redfearn wrote:
>> Hi Marc,
>>
>> On 07/02/18 09:41, Marc Zyngier wrote:
>>> On 05/02/18 16:45, Matt Redfearn wrote:
>>>> Commit 7778c4b27cbe ("irqchip: mips-gic: Use pcpu_masks to avoid reading
>>>> GIC_SH_MASK*") removed the read of the hardware mask register when
>>>> handling shared interrupts, instead using the driver's shadow pcpu_masks
>>>> entry as the effective mask. Unfortunately this did not take account of
>>>> the write to pcpu_masks during gic_shared_irq_domain_map, which
>>>> effectively unmasks the interrupt early. If an interrupt is asserted,
>>>> gic_handle_shared_int decodes and processes the interrupt even though it
>>>> has not yet been unmasked via gic_unmask_irq, which also sets the
>>>> appropriate bit in pcpu_masks.
>>>>
>>>> On the MIPS Boston board, when a console command line of
>>>> "console=ttyS0,115200n8r" is passed, the modem status IRQ is enabled in
>>>> the UART, which is immediately raised to the GIC. The interrupt has been
>>>> mapped, but no handler has yet been registered, nor is it expected to be
>>>> unmasked. However, the write to pcpu_masks in gic_shared_irq_domain_map
>>>> has effectively unmasked it, resulting in endless reports of:
>>>>
>>>> [    5.058454] irq 13, desc: ffffffff80a7ad80, depth: 1, count: 0, unhandled: 0
>>>> [    5.062057] ->handle_irq():  ffffffff801b1838,
>>>> [    5.062175] handle_bad_irq+0x0/0x2c0
>>>>
>>>> Where IRQ 13 is the UART interrupt.
>>>>
>>>> To fix this, just remove the write to pcpu_masks in
>>>> gic_shared_irq_domain_map. The existing write in gic_unmask_irq is the
>>>> correct place for what is now the effective unmasking.
>>>>
>>>> Fixes: 7778c4b27cbe ("irqchip: mips-gic: Use pcpu_masks to avoid reading GIC_SH_MASK*")
>>>> Signed-off-by: Matt Redfearn <matt.redfearn@...s.com>
>>>> Reviewed-by: Paul Burton <paul.burton@...s.com>
>>>>
>>>> ---
>>>>
>>>>    drivers/irqchip/irq-mips-gic.c | 2 --
>>>>    1 file changed, 2 deletions(-)
>>>>
>>>> diff --git a/drivers/irqchip/irq-mips-gic.c b/drivers/irqchip/irq-mips-gic.c
>>>> index b2cfc6d66d74..2c3684ba46e5 100644
>>>> --- a/drivers/irqchip/irq-mips-gic.c
>>>> +++ b/drivers/irqchip/irq-mips-gic.c
>>>> @@ -429,8 +429,6 @@ static int gic_shared_irq_domain_map(struct irq_domain *d, unsigned int virq,
>>>>    	spin_lock_irqsave(&gic_lock, flags);
>>>>    	write_gic_map_pin(intr, GIC_MAP_PIN_MAP_TO_PIN | shared_cpu_pin);
>>>>    	write_gic_map_vp(intr, BIT(mips_cm_vp_id(cpu)));
>>>> -	gic_clear_pcpu_masks(intr);
>>>> -	set_bit(intr, per_cpu_ptr(pcpu_masks, cpu));
>>>>    	irq_data_update_effective_affinity(data, cpumask_of(cpu));
>>>>    	spin_unlock_irqrestore(&gic_lock, flags);
>>>>    
>>>>
>>>
>>> Does this need to be Cc to stable (since it fixes something that was
>>> merged in 4.14)?
>>
>> Sorry, missed stable off the CC list. Yes, it does indeed need to be
>> backported. Should I resubmit?
> No need, I'll add that to the patch.

Great, thanks!
Matt

> 
> Thanks,
> 
> 	M.
>