linux-kernel - Re: [PATCH] acpi/rt: convert acpi_gbl_gpe

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Date:   Fri, 2 Dec 2016 11:00:48 -0600 (CST)
From:   Aaron Sierra <asierra@...-inc.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] acpi/rt: convert acpi_gbl_gpe_lock to raw spinlock

----- Original Message -----
> From: "Thomas Gleixner" <tglx@...utronix.de>
> Sent: Thursday, December 1, 2016 5:21:20 PM

> On Thu, 1 Dec 2016, Aaron Sierra wrote:
>> ----- Original Message -----
>> > From: "Thomas Gleixner" <tglx@...utronix.de>
>> > Sent: Thursday, December 1, 2016 8:52:48 AM
>> 
>> > On Wed, 30 Nov 2016, Aaron Sierra wrote:
>> >> When testing GPE interrupts with CONFIG_PREEMPT_RT_FULL enabled, a
>> >> verbose WARN_ONCE message would print to the kernel log. It turned out
>> >> that the GPE interrupt handler was being called with local interrupts
>> >> enabled because acpi_gbl_gpe_lock was implemented as a spinlock_t. Full
>> >> preemption strips local interrupt disabling from spinlock_t operations,
>> >> but not for raw_spinlock_t operations.
>> >> 
>> >> This is the warning that was triggered:
>> >> 
>> >> ------------[ cut here ]------------
>> >> WARNING: CPU: 8 PID: 483 at kernel/irq/handle.c:149
>> >> __handle_irq_event_percpu+0x6f/0xcf
>> >> irq 33 handler irq_default_primary_handler+0x0/0xb enabled interrupts
>> >> Modules linked in: gpio_irq_demo(O)
>> >> CPU: 8 PID: 483 Comm: irq/9-acpi Tainted: G           O
>> >> 4.8.6-rt5-00012-geaa3b7c #6
>> >> Hardware name: Extreme Engineering Solutions, Inc. XCalibur4643/XCalibur4643,
>> >> BIOS 1-1.1.12.3_Alpha 04/29/2016
>> >>  0000000000000000 ffff880858f3bc10 ffffffff81219a93 ffff880858f3bc60
>> >>  0000000000000000 ffff880858f3bc50 ffffffff8104b84a 0000009500000000
>> >>  ffff880855b76880 0000000000000021 0000000000000002 ffff880856356800
>> >> Call Trace:
>> >>  [<ffffffff81219a93>] dump_stack+0x4d/0x63
>> >>  [<ffffffff8104b84a>] __warn+0xc0/0xdb
>> >>  [<ffffffff8104b8af>] warn_slowpath_fmt+0x4a/0x4c
>> >>  [<ffffffff810f7192>] ? path_openat+0xbf8/0xc62
>> >>  [<ffffffff8107d7c3>] ? handle_irq_event+0x75/0x75
>> >>  [<ffffffff8107d68d>] __handle_irq_event_percpu+0x6f/0xcf
>> >>  [<ffffffff8107d727>] handle_irq_event_percpu+0x3a/0x61
>> >>  [<ffffffff8107d7a3>] handle_irq_event+0x55/0x75
>> >>  [<ffffffff8107ff76>] handle_simple_irq+0x5c/0x92
>> >>  [<ffffffff81243a53>] gpe_irq_handler+0x2a/0x31
>> > 
>> > gpe_irq_handler is not in tree, so I really cannot tell what this is
>> > about. It looks like it does interrupt demultiplexing, which triggers the
>> > warning.
>> 
>> Thomas,
>> Your guess is correct, this involves a currently out-of-tree extension to
>> the gpio-ich driver which allows GPIO pins to be mapped to IRQs by demuxing
>> their corresponding GPE events.
>> The gpio_irq_demo module requests a GPIO pin, converts it to an IRQ using
>> gpio_to_irq() and registers a trivial handler against the IRQ.
> 
> So the simple solution is in the demux handler:
> 
> gpe_irq_handler()
> {
> +	local_irq_save(flags);
> 
>	for_each_pending_gpio_irq(irq)
>		generic_handle_irq(irq);
> 
> +	local_irq_restore(flags);
> }

Thomas,
Yes, of course. That's how I initially worked around my problem before
digging into the ACPI subsystem. I just didn't believe that was anything
more than a workaround, so I went looking for a more "correct" solution.
I don't have a problem maintaining this for myself if it isn't generally
useful.

-Aaron S.