linux-kernel - Re: [PATCH 1/2] clk: imx: do not sleep if IRQ's are still disabled

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Date:	Wed, 25 May 2016 14:54:07 -0700
From:	Stefan Agner <stefan@...er.ch>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Dong Aisheng <dongas86@...il.com>, Shawn Guo <shawnguo@...nel.org>,
	Lucas Stach <l.stach@...gutronix.de>,
	Michael Turquette <mturquette@...libre.com>,
	Stephen Boyd <sboyd@...eaurora.org>,
	linux-kernel@...r.kernel.org, mingo@...hat.com,
	kernel@...gutronix.de, linux-clk@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 1/2] clk: imx: do not sleep if IRQ's are still disabled

On 2016-04-27 03:15, Thomas Gleixner wrote:
> On Wed, 27 Apr 2016, Dong Aisheng wrote:
>> Why Stefan's patch works (checking irqs_disabled()) is because during kernel
>> time init, the irq is still not enabled. It fixes the issue indirectly.
>> See:
>> asmlinkage __visible void __init start_kernel(void)
>> {
>>         /*
>>          * Set up the scheduler prior starting any interrupts (such as the
>>          * timer interrupt). Full topology setup happens at smp_init()
>>          * time - but meanwhile we still have a functioning scheduler.
>>          */
>>         sched_init();
>>         .............
>>         time_init();
>>         ..............
>>         WARN(!irqs_disabled(), "Interrupts were enabled early\n");
>>         early_boot_irqs_disabled = false;
>>         local_irq_enable();
>> }
>>
>> The issue can only happen when PLL enable causes a schedule during
>> imx_clock_init().
> 
> Calling a function which might sleep _BEFORE_ kernel_init() is wrong. Don't
> try to work around such an issue by doing magic irq_disabled() checks and busy
> loops. Fix the call site and be done with it.

What do you mean exactly by fix the call site? The patch I proposed
(https://lkml.org/lkml/2016/1/29/695) fixes the call site...

But I see Dong's argument here, irqs_disabled is the wrong way to figure
out whether we are in kernel_init. What is the right approach to
distinguish whether we are allowed to sleep?

--
Stefan