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]().
Signed-off-by: Lecopzer Chen <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Marc Zyngier <[email protected]>
Cc: Julien Thierry <[email protected]>
Cc: YJ Chiang <[email protected]>
Cc: Lecopzer Chen <[email protected]>
---
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)
--
2.18.0
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 <[email protected]>
> Cc: Thomas Gleixner <[email protected]>
> Cc: Peter Zijlstra <[email protected]>
> Cc: Ingo Molnar <[email protected]>
> Cc: Marc Zyngier <[email protected]>
> Cc: Julien Thierry <[email protected]>
> Cc: YJ Chiang <[email protected]>
> Cc: Lecopzer Chen <[email protected]>
> ---
> 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...
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
Thanks a lot for reply!!
I just misunderstood how a PPI is registered and thought
I have a chance to eliminate the code.
This patch seems nonsense now, please ignore it.
Sorry to disturb you guys.
Thanks,
Lecopzer