linux-kernel - Re: [PATCH] generic: Add the exception case checking routine for ppi interrupt

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Message-ID: <57C99F8D.9080503@arm.com>
Date:   Fri, 2 Sep 2016 16:49:33 +0100
From:   Marc Zyngier <marc.zyngier@....com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     "majun (F)" <majun258@...wei.com>,
        Mark Rutland <mark.rutland@....com>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        dingtianhong@...wei.com, guohanjun@...wei.com
Subject: Re: [PATCH] generic: Add the exception case checking routine for ppi
 interrupt

On 02/09/16 14:08, Thomas Gleixner wrote:
> On Thu, 1 Sep 2016, Marc Zyngier wrote:
>> On 01/09/16 09:15, majun (F) wrote:
>> Well, this issue goes way beyond the hack you wanted to add to the
>> generic code, and it should probably be addressed in the GIC code
>> itself, as an implementation specific workaround. Without knowing the
>> details of the erratum, it is difficult to think of that would be
>> required. I can come up with something like this:
>>
>> 	irqnr = gic_read_iar();
>> 	if (unlikely(!is_enabled(irqnr))) {
>> 		gic_write_eoir(irqnr);
>> 		if (static_key_true(&supports_deactivate))
>> 			gic_write_dir(irqnr);
>> 		set_pending(irqnr);
>> 		continue;
>> 	}
>>
>> Performance will suffer (an extra MMIO access on the fast path). If LPIs
>> are also affected, then the ITS code also needs to be involved, and
>> that's not going to be pretty either. This code will have to be enabled
>> at runtime, and handled like other erratum we have in this code.
> 
> So that's certainly a required workaround at the gic level. Though I really
> think that we should make handle_percpu_devid_irq robust against a spurious
> interrupt.
> 
>>  void handle_percpu_devid_irq(unsigned int irq, struct irq_desc *desc)
>>  {
>> -	struct irq_chip *chip = irq_desc_get_chip(desc);
>> -	struct irqaction *action = desc->action;
>> -	void *dev_id = raw_cpu_ptr(action->percpu_dev_id);
>> +	struct irq_chip *chip = NULL;
>> +	struct irqaction *action;
>> +	void *dev_id;
>>  	irqreturn_t res;
>>  
>> +	action = desc->action;
>> +
>> +	/* Unexpected interrupt in some execption case
>> +	 * we just send eoi to end this interrupt
>> +	 */
>> +	if (unlikely(!action)) {
>> +		mask_irq(desc);
> 
> This is wrong. mask_irq() does not work for percpu interrupts. Aside of that
> this completely lacks any debug information which tells us that there is
> something wrong in the system. I'm going to apply the patch below for
> robustness sake.
> 
> Thanks,
> 
> 	tglx
> 
> 8<----------------------
> Subject: genirq: Robustify handle_percpu_devid_irq()
> From: Thomas Gleixner <tglx@...utronix.de>
> Date: Fri, 02 Sep 2016 14:45:19 +0200
> 
> The percpu_devid handler is not robust against spurious interrupts. If a
> spurious interrupt happens and no action is installed then the handler crashes
> with a NULL pointer dereference.
> 
> Add a sanity check for this and log the wreckage once in dmesg.
> 
> Reported-by: Majun <majun258@...wei.com>
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>

Looks fine to me.

Acked-by: Marc Zyngier <marc.zyngier@....com>

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