Re: [RFC PATCH kernel] powerpc/xive: Drop deregistered irqs

From: Alexey Kardashevskiy <aik@ozlabs.ru>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	linuxppc-dev@lists.ozlabs.org
Cc: "Greg Kurz" <groug@kaod.org>,
	"Nicholas Piggin" <npiggin@gmail.com>,
	"Paul Mackerras" <paulus@samba.org>,
	"Cédric Le Goater" <clg@kaod.org>,
	"Alistair Popple" <alistair@popple.id.au>,
	"David Gibson" <david@gibson.dropbear.id.au>
Subject: Re: [RFC PATCH kernel] powerpc/xive: Drop deregistered irqs
Date: Fri, 12 Jul 2019 19:37:16 +1000	[thread overview]
Message-ID: <3a34190f-560e-0b42-af38-0e39cef0beea@ozlabs.ru> (raw)
In-Reply-To: <abbee9db2fa0abdaa2e01bb92bab920773a2ad8d.camel@kernel.crashing.org>

On 12/07/2019 18:29, Benjamin Herrenschmidt wrote:
> On Fri, 2019-07-12 at 18:20 +1000, Alexey Kardashevskiy wrote:
>>
>> diff --git a/arch/powerpc/sysdev/xive/common.c b/arch/powerpc/sysdev/xive/common.c
>> index 082c7e1c20f0..65742e280337 100644
>> --- a/arch/powerpc/sysdev/xive/common.c
>> +++ b/arch/powerpc/sysdev/xive/common.c
>> @@ -148,8 +148,12 @@ static u32 xive_scan_interrupts(struct xive_cpu *xc, bool just_peek)
>>   		irq = xive_read_eq(&xc->queue[prio], just_peek);
>>   
>>   		/* Found something ? That's it */
>> -		if (irq)
>> -			break;
>> +		if (irq) {
>> +			/* Another CPU may have shut this irq down, check it */
>> +			if (irq_to_desc(irq))
> 
> What if it gets deregistered here .... ?

Yeah that is the problem.

> 
>> +				break;
>> +			irq = 0;
>> +		}
>>   
>>   		/* Clear pending bits */
>>   		xc->pending_prio &= ~(1 << prio);
> 
> Wouldn't it be better to check the return value from generic_handle_irq
> instead ?

Where exactly, here?
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/powerpc/kernel/irq.c#n614

If so, then in order to do EOI, I'll need the desc which is gone, or I 
am missing the point?

-- 
Alexey