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Date: Thu, 20 Jun 2019 10:40:39 +0100 From: Marc Zyngier <marc.zyngier@....com> To: Lecopzer Chen <lecopzer.chen@...iatek.com>, linux-kernel@...r.kernel.org Cc: linux-arm-kernel@...ts.infradead.org, Thomas Gleixner <tglx@...utronix.de>, Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...nel.org>, Julien Thierry <julien.thierry@....com>, YJ Chiang <yj.chiang@...iatek.com> Subject: Re: [PATCH] genirq: Remove warning on preemptible in prepare_percpu_nmi() Hi Lecopzer, On 20/06/2019 10:12, Lecopzer Chen wrote: > prepare_percpu_nmi() acquires lock first by irq_get_desc_lock(), > no matter whether preempt enabled or not, acquiring lock forces preempt off. > > This simplifies the usage of prepare_percpu_nmi() and we don't need to > acquire extra lock or explicitly call preempt_[disable,enable](). I strongly disagree. If you're calling these functions *from* a preemptible context, you've already lost, and that's what these WARN_ON() calls are warning you about. These functions can only be called from a context that is naturally preemption free, such as a hotplug notifier. Otherwise, you have no idea which CPU you're configuring the NMI on, and I cannot see that as a good thing. Thanks, M. > > Signed-off-by: Lecopzer Chen <lecopzer.chen@...iatek.com> > Cc: Thomas Gleixner <tglx@...utronix.de> > Cc: Peter Zijlstra <peterz@...radead.org> > Cc: Ingo Molnar <mingo@...nel.org> > Cc: Marc Zyngier <marc.zyngier@....com> > Cc: Julien Thierry <julien.thierry@....com> > Cc: YJ Chiang <yj.chiang@...iatek.com> > Cc: Lecopzer Chen <lecopzer.chen@...iatek.com> > --- > kernel/irq/manage.c | 10 ---------- > 1 file changed, 10 deletions(-) > > diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c > index 78f3ddeb7fe4..aa03640cd7fb 100644 > --- a/kernel/irq/manage.c > +++ b/kernel/irq/manage.c > @@ -2509,9 +2509,6 @@ int request_percpu_nmi(unsigned int irq, irq_handler_t handler, > * This call prepares an interrupt line to deliver NMI on the current CPU, > * before that interrupt line gets enabled with enable_percpu_nmi(). > * > - * As a CPU local operation, this should be called from non-preemptible > - * context. > - * > * If the interrupt line cannot be used to deliver NMIs, function > * will fail returning a negative value. > */ > @@ -2521,8 +2518,6 @@ int prepare_percpu_nmi(unsigned int irq) > struct irq_desc *desc; > int ret = 0; > > - WARN_ON(preemptible()); > - > desc = irq_get_desc_lock(irq, &flags, > IRQ_GET_DESC_CHECK_PERCPU); > if (!desc) > @@ -2554,17 +2549,12 @@ int prepare_percpu_nmi(unsigned int irq) > * This call undoes the setup done by prepare_percpu_nmi(). > * > * IRQ line should not be enabled for the current CPU. > - * > - * As a CPU local operation, this should be called from non-preemptible > - * context. > */ > void teardown_percpu_nmi(unsigned int irq) > { > unsigned long flags; > struct irq_desc *desc; > > - WARN_ON(preemptible()); > - > desc = irq_get_desc_lock(irq, &flags, > IRQ_GET_DESC_CHECK_PERCPU); > if (!desc) > -- Jazz is not dead. It just smells funny...
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