linux-kernel - Re: [PATCH] perf/arm-cmn: Add shutdown routine

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Message-ID: <c7acc1af-b97e-f9f7-4891-64bc9380a12e@arm.com>
Date:   Wed, 30 Nov 2022 12:28:17 +0000
From:   Robin Murphy <robin.murphy@....com>
To:     Will Deacon <will@...nel.org>, Geoff Blake <blakgeof@...zon.com>,
        linux-kernel@...r.kernel.org
Cc:     catalin.marinas@....com, kernel-team@...roid.com,
        linux-arm-kernel@...ts.infradead.org,
        Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH] perf/arm-cmn: Add shutdown routine

On 2022-11-29 19:52, Will Deacon wrote:
> On Fri, 25 Nov 2022 17:01:53 -0600, Geoff Blake wrote:
>> The CMN driver does not gracefully handle all
>> restart cases, such as kexec.  On a kexec if the
>> arm-cmn driver is in use it can be left in a state
>> with still active  events that can cause spurious and/or
>> unhandled interrupts that appear as non-fatal kernel errors
>> like below, that can be confusing and misleading:
>>
>> [...]
> 
> Applied to will (for-next/perf), thanks!
> 
> [1/1] perf/arm-cmn: Add shutdown routine
>        https://git.kernel.org/will/c/316f862a787c

Oh, if I'd seen this I'd have said the same thing as when asked about it 
off-list, that it's needlessly overcomplicated and doesn't really solve 
the problem anyway. If there's a need to be robust against spurious 
interrupts then that needs to be done in the interrupt handler.

Even if we do think it's worth stopping the PMU on shutdown, as we do on 
remove, that still only needs a single register write (per the current 
remove implementation).

Thanks,
Robin.