Re: [RFC PATCH 25/36] arm_mpam: Register and enable IRQs

[Jonathan Cameron <Jonathan.Cameron@huawei.com>]

On Fri, 11 Jul 2025 18:36:37 +0000
James Morse <james.morse@arm.com> wrote:

> Register and enable error IRQs. All the MPAM error interrupts indicate a
> software bug, e.g. out of range partid. If the error interrupt is ever
> signalled, attempt to disable MPAM.
> 
> Only the irq handler accesses the ESR register, so no locking is needed.
> The work to disable MPAM after an error needs to happen at process
> context, use a threaded interrupt.
> 
> There is no support for percpu threaded interrupts, for now schedule
> the work to be done from the irq handler.
> 
> Enabling the IRQs in the MSC may involve cross calling to a CPU that
> can access the MSC.
> 
> CC: Rohit Mathew <rohit.mathew@arm.com>
> Tested-by: Rohit Mathew <rohit.mathew@arm.com>
> Signed-off-by: James Morse <james.morse@arm.com>
Sparse gives an imbalance warning in mpam_register_irqs()

> +static int mpam_register_irqs(void)
> +{
> +	int err, irq, idx;
> +	struct mpam_msc *msc;
> +
> +	lockdep_assert_cpus_held();
> +
> +	idx = srcu_read_lock(&mpam_srcu);
> +	list_for_each_entry_srcu(msc, &mpam_all_msc, glbl_list, srcu_read_lock_held(&mpam_srcu)) {
> +		irq = platform_get_irq_byname_optional(msc->pdev, "error");
> +		if (irq <= 0)
> +			continue;
> +
> +		/* The MPAM spec says the interrupt can be SPI, PPI or LPI */
> +		/* We anticipate sharing the interrupt with other MSCs */
> +		if (irq_is_percpu(irq)) {
> +			err = request_percpu_irq(irq, &mpam_ppi_handler,
> +						 "mpam:msc:error",
> +						 msc->error_dev_id);
> +			if (err)
> +				return err;

Looks like the srcu_read_lock is still held.

There is a DEFINE_LOCK_GUARD_1() in srcu.h so you can do

	guard(srcu)(&mpam_srcu, idx);

I think and not worry about releasing it in errors or the good path.

> +
> +			msc->reenable_error_ppi = irq;
> +			smp_call_function_many(&msc->accessibility,
> +					       &_enable_percpu_irq, &irq,
> +					       true);
> +		} else {
> +			err = devm_request_threaded_irq(&msc->pdev->dev, irq,
> +							&mpam_spi_handler,
> +							&mpam_disable_thread,
> +							IRQF_SHARED,
> +							"mpam:msc:error", msc);
> +			if (err)
> +				return err;
> +		}
> +
> +		msc->error_irq_requested = true;
> +		mpam_touch_msc(msc, mpam_enable_msc_ecr, msc);
> +		msc->error_irq_hw_enabled = true;
> +	}
> +	srcu_read_unlock(&mpam_srcu, idx);
> +
> +	return 0;
> +}