linux-kernel - Re: [PATCH 1/1] Revert "genirq: Remove the second parameter from handle_irq_event

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Date:	Mon, 18 Jan 2016 16:00:12 +0800
From:	zhuyj <zyjzyj2000@...il.com>
To:	Huang Shijie <shijie.huang@....com>,
	Thomas Gleixner <tglx@...utronix.de>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Jiang Liu <jiang.liu@...ux.intel.com>,
	Peter Zijlstra <peterz@...radead.org>, nd@....com
Subject: Re: [PATCH 1/1] Revert "genirq: Remove the second parameter from
 handle_irq_event_percpu()"

Hi, all

I made tests for this patch. To now, I can not find any similar problem.

Best Regards!
Zhu Yanjun

On 01/14/2016 09:29 AM, Huang Shijie wrote:
> On Wed, Jan 13, 2016 at 02:07:25PM +0100, Thomas Gleixner wrote:
>> On Wed, 13 Jan 2016, zyjzyj2000@...il.com wrote:
>>
>>> After this commit 71f64340fc0e ("genirq: Remove the second parameter
>>> from handle_irq_event_percpu()") is applied, the variable action is
>>> not protected by raw_spin_lock. The following calltrace will pop up.
>> Thanks, for the report. I missed that detail when merging the patch!
>>
>> Just for correctness sake: You miss to explain why this can happen.
>>
>> It's not about the variable action, it's about desc->action not being
>> protected anymore. So the reason why this oopses is that the action is being
>> removed concurrently.
>>
>> CPU 0			CPU 1
>>
>> free_irq()		lock(desc)
>> lock(desc)		handle_edge_irq()
>> 			  handle_irq_event(desc)
>> 			    unlock(desc)
>> desc->action = NULL	    handle_irq_event_percpu(desc)
>> 	       		      action = desc->action
>>
>> While the original code did:
>>
>> free_irq()		lock(desc)
>> lock(desc)		handle_edge_irq()
>> 			  handle_irq_event()
>> 	       		    action = desc->action
>> 			    unlock(desc)
>> desc->action = NULL	    handle_irq_event_percpu(desc, action)
>> 	       		
>> So now the question is whether we revert that patch or simply change
>> handle_irq_event_percpu() to deal with that. Patch below.
>>
>> That preserves us the code size reduction of commit 71f64340fc0e. This is safe
>> because we either see a valid desc->action or NULL. If the action is about to
>> be removed it is still valid as free_irq() is blocked on synchronize_irq().
>>
>> free_irq()		lock(desc)
>> lock(desc)		handle_edge_irq()
>> 			  handle_irq_event(desc)
>> 			    set(INPROGRESS)
>> 			    unlock(desc)
>> 			      handle_irq_event_percpu(desc)
>> 	       		        action = desc->action
>> desc->action = NULL
>> sychronize_irq()
>>    while(INPROGRESS);	   lock(desc)
>> 			   clr(INPROGRESS)
>> free(action)
>>
>> That's basically the same mechanism as we have for shared
>> interrupts. action->next can become NULL while handle_irq_event_percpu()
>> runs. Either it sees the action or NULL. It does not matter, because action
>> itself cannot go away.
>>
>> Thanks,
>>
>> 	tglx
>>
>> 8<-------------
>>
>> --- a/kernel/irq/handle.c
>> +++ b/kernel/irq/handle.c
>> @@ -136,9 +136,15 @@ irqreturn_t handle_irq_event_percpu(stru
>>   {
>>   	irqreturn_t retval = IRQ_NONE;
>>   	unsigned int flags = 0, irq = desc->irq_data.irq;
>> -	struct irqaction *action = desc->action;
>> +	struct irqaction *action;
>>   
>> -	do {
>> +	/*
>> +	 * READ_ONCE is not required here. The compiler cannot reload action
>> +	 * because it'll be action->next for the second iteration of the loop.
>> +	 */
>> +	action = desc->action;
>> +
>> +	while (action) {
>>   		irqreturn_t res;
>>   
>>   		trace_irq_handler_entry(irq, action);
>> @@ -173,7 +179,7 @@ irqreturn_t handle_irq_event_percpu(stru
>>   
>>   		retval |= res;
>>   		action = action->next;
>> -	} while (action);
>> +	}
>>   
>>   	add_interrupt_randomness(irq, flags);
> I prefer to this patch, revert the old the patch is not a good solution.
>
> thanks
> Huang Shijie
>