Re: [PATCH v2] genirq: Check irq disabled & masked states in irq_shutdown

From: jeffy
Date: Sat May 27 2017 - 06:09:42 EST


Hi Thomas,

On 05/27/2017 04:30 PM, Thomas Gleixner wrote:
On Sat, 27 May 2017, Jeffy Chen wrote:

If a irq is already disabled & masked, free_irq may cause a unbalanced
irq shutdown/disable/mask, for example:

No, it's not. irq_shutdown/disable/mask are low level access functions
which can be invoked at any given time.

The only interface which has refcounting is disable/enable_irq().
but i think it still be good trying to make them balance, at least for irq enable/disable :)

devm_request_irq->irq_startup->irq_enable
disable_irq <-- disabled and masked
devm_free_irq->irq_shutdown <-- try to disable it again

This would confuse some pinctrl drivers which would control clk in
irq_enable/irq_disable, for example pinctrl-rockchip/pinctrl-nomadik.

This patch add a state check in irq_shutdown to prevent that.

Please read Documentation/process/SubmittingPatches and search for "this
patch".
oops

diff --git a/kernel/irq/chip.c b/kernel/irq/chip.c
index 686be4b..816da03 100644
--- a/kernel/irq/chip.c
+++ b/kernel/irq/chip.c
@@ -206,14 +206,20 @@ int irq_startup(struct irq_desc *desc, bool resend)

void irq_shutdown(struct irq_desc *desc)
{
- irq_state_set_disabled(desc);
desc->depth = 1;
+
+ if (unlikely(irqd_irq_disabled(&desc->irq_data) &&
+ irqd_irq_masked(&desc->irq_data)))
+ goto out;

This is just wrong.

It's perfectly legit to call disable_irq() and then free_irq(). Still
free_irq() has to be able to invoke chip->irq_shutdown(). Preventing that
will leave some interrupt chips in a half initialized state.
right, irq_shutdown is not just to disable irq, may also do some cleanups. will upload new patch.

The irq core does not guarntee that the unmask/mask enable/disable
startup/shutdown callbacks are perfectly balanced. irq_shutdown() is only
one place where this can happen. This needs more thought than this 'works
for me' hackery.

Thanks,

tglx