Messages in this thread | | | Subject | Re: [PATCH] genirq: Remove warning on preemptible in prepare_percpu_nmi() | From | Julien Thierry <> | Date | Thu, 20 Jun 2019 10:44:22 +0100 |
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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](). >
This allows wrong usage of prepare_percpu_nmi(). If you are not calling it from a preemptible context, you could start the call on a CPU, get preempted and setup the NMI on a completely different CPU than the one you started on.
This check is for sanity checking, and if you end up calling prepare_percpu_nmi() from non-preemptible context then your intentions are unclear, unless you are fine with the possibility of "preparing an NMI on a random CPU". Also you would have no way to know that that CPU (since you could run on a random CPU) doesn't already have that IRQ line set for NMI delivery.
So, I don't think removing those simplifies much, it just silences calls to it that could go wrong.
Cheers,
-- Julien Thierry
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