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.c...@mediatek.com>
> Cc: Thomas Gleixner <t...@linutronix.de>
> Cc: Peter Zijlstra <pet...@infradead.org>
> Cc: Ingo Molnar <mi...@kernel.org>
> Cc: Marc Zyngier <marc.zyng...@arm.com>
> Cc: Julien Thierry <julien.thie...@arm.com>
> Cc: YJ Chiang <yj.chi...@mediatek.com>
> Cc: Lecopzer Chen <lecopzer.c...@mediatek.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...
