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[98.179.76.75]) by smtp.gmail.com with ESMTPSA id o5sm565190qti.47.2020.12.06.13.47.46 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 06 Dec 2020 13:47:46 -0800 (PST) References: <20201205014340.148235-1-jsnitsel@redhat.com> <20201205014340.148235-3-jsnitsel@redhat.com> <875z5e99ez.fsf@nanos.tec.linutronix.de> User-agent: mu4e 1.4.10; emacs 27.1 From: Jerry Snitselaar To: Thomas Gleixner Cc: linux-kernel@vger.kernel.org, linux-integrity@vger.kernel.org, intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, Jani Nikula , Rodrigo Vivi , David Airlie , Daniel Vetter , Jarkko Sakkinen , Jason Gunthorpe , Peter Huewe , James Bottomley , Matthew Garrett , Hans de Goede , Peter Zijlstra 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> Date: Sun, 06 Dec 2020 14:47:45 -0700 Message-ID: <87im9ehaim.fsf@redhat.com> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Thomas Gleixner @ 2020-12-06 09:38 MST: > 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 >> --- a/drivers/gpu/drm/i915/i915_pmu.c >> +++ b/drivers/gpu/drm/i915/i915_pmu.c >> @@ -423,22 +423,6 @@ static enum hrtimer_restart i915_sample(struct hrtimer *hrtimer) >> return HRTIMER_RESTART; >> } >> >> -static u64 count_interrupts(struct drm_i915_private *i915) >> -{ >> - /* open-coded kstat_irqs() */ >> - struct irq_desc *desc = irq_to_desc(i915->drm.pdev->irq); >> - u64 sum = 0; >> - int cpu; >> - >> - if (!desc || !desc->kstat_irqs) >> - return 0; >> - >> - for_each_possible_cpu(cpu) >> - sum += *per_cpu_ptr(desc->kstat_irqs, cpu); >> - >> - return sum; >> -} > > 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. > > Thanks, > > tglx I don't know the history behind this bit. I stumbled across it in cscope when looking for places using kstat_irqs.