linux-kernel - Re: [v4.1.10-rt10][PATCH 1/2] genirq: introduce new generic_handle_irq_rt

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Date:	Mon, 2 Nov 2015 20:38:20 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Grygorii Strashko <grygorii.strashko@...com>
cc:	bigeasy@...utronix.de, linux-rt-users@...r.kernel.org,
	linux-kernel@...r.kernel.org, Sekhar Nori <nsekhar@...com>
Subject: Re: [v4.1.10-rt10][PATCH 1/2] genirq: introduce new generic_handle_irq_rt_wa()
 api

On Mon, 2 Nov 2015, Grygorii Strashko wrote:
> Now in kernel below code pattern is used by many drivers:
> static irqreturn_t driver_xx_hw_irq_handler(int irq, void *arg)
> {
> 	<read IRQ status register>
>   	<perform HW specific operations>
> 
> 	for (<each set bit in IRQ status register>) {
> 		<get Linux IRQ number>
> 		generic_handle_irq(<Linux IRQ number>);
> 		|- handle_simple_irq()
> 		|-or- handle_level_irq()
> 		|-or- handle_edge_irq()
> 		   |-handle_irq_event()
> 		     |-handle_irq_event_percpu()
> ===
> "WARNING: CPU: 1 PID: 82 at kernel/irq/handle.c:150 handle_irq_event_percpu+0x14c/0x174()
>  irq 460 handler irq_default_primary_handler+0x0/0x14 enabled interrupts"
> ===
> 	}
> }
> 
> On -RT above code will generate warnings, because driver_xx_hw_irq_handler()
> will be forced threaded (by default) and, as result, generic_handle_irq()
> will be called with IRQs enabled. To W/A this issue generic_handle_irq() can
> be surrounded by raw_spin_lock_irqsave/irqrestore(wa_lock).
> 
> Instead of spreading this W/A directly in many drivers this patch
> introduces -RT specific version of generic_handle_irq() API -
> generic_handle_irq_rt_wa(). This new generic_handle_irq_rt_wa() just calls
> generic_handle_irq() surrounded by raw_spin_lock_irqsave/irqrestore().
> If -RT is disabled It will fallback to generic_handle_irq().

Why aren't you simply marking these demultiplex handlers with IRQ_NO_THREAD?

Thanks,

	tglx
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