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

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Date:   Wed, 7 Feb 2018 10:41:17 +0000
From:   Marc Zyngier <marc.zyngier@....com>
To:     Matt Redfearn <matt.redfearn@...s.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

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.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...