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From:   Thomas Gleixner <tglx@linutronix.de>
To:     Jerry Snitselaar <jsnitsel@redhat.com>,
        linux-kernel@vger.kernel.org
Cc:     linux-integrity@vger.kernel.org, intel-gfx@lists.freedesktop.org,
        dri-devel@lists.freedesktop.org,
        Jani Nikula <jani.nikula@linux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@intel.com>,
        David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>,
        Jarkko Sakkinen <jarkko@kernel.org>,
        Jason Gunthorpe <jgg@ziepe.ca>,
        Peter Huewe <peterhuewe@gmx.de>,
        James Bottomley <James.Bottomley@HansenPartnership.com>,
        Matthew Garrett <mjg59@google.com>,
        Hans de Goede <hdegoede@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH v3 2/4] drm/i915/pmu: Use kstat_irqs to get interrupt count
In-Reply-To: <875z5e99ez.fsf@nanos.tec.linutronix.de>
References: <20201205014340.148235-1-jsnitsel@redhat.com> <20201205014340.148235-3-jsnitsel@redhat.com> <875z5e99ez.fsf@nanos.tec.linutronix.de>
Date:   Sun, 06 Dec 2020 22:33:09 +0100
Message-ID: <87o8j67h7u.fsf@nanos.tec.linutronix.de>
MIME-Version: 1.0
Content-Type: text/plain
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On Sun, Dec 06 2020 at 17:38, Thomas Gleixner wrote:
> On Fri, Dec 04 2020 at 18:43, Jerry Snitselaar wrote:
>> Now that kstat_irqs is exported, get rid of count_interrupts in
>> i915_pmu.c
>
> May I ask why this has been merged in the first place?
>
> Nothing in a driver has ever to fiddle with the internals of an irq
> descriptor. We have functions for properly accessing them. Just because
> C allows to fiddle with everything is not a justification. If the
> required function is not exported then adding the export with a proper
> explanation is not asked too much.
>
> Also this lacks protection or at least a comment why this can be called
> safely and is not subject to a concurrent removal of the irq descriptor.
> The same problem exists when calling kstat_irqs(). It's even documented
> at the top of the function.

And as pointed out vs. that TPM thing this really could have been a
trivial

    i915->irqs++;

in the interrupt handler and a read of that instead of iterating over
all possible cpus and summing it up. Oh well...

Thanks,

        tglx