linux-kernel - Re: [PATCH 3/3] kernel/irq/manage.c: disable

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Date:   Fri, 23 Dec 2022 11:54:29 +0100
From:   Manfred Spraul <manfred@...orfullife.com>
To:     "Sverdlin, Alexander" <alexander.sverdlin@...mens.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>
Cc:     "1vier1@....de" <1vier1@....de>,
        "tglx@...utronix.de" <tglx@...utronix.de>
Subject: Re: [PATCH 3/3] kernel/irq/manage.c: disable_irq() might sleep.

Hi Alexander,

On 12/20/22 07:58, Sverdlin, Alexander wrote:
> Hi Manfred!
>
> On Fri, 2022-12-16 at 16:04 +0100, Manfred Spraul wrote:
>> diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
>> index 5b7cf28df290..8ce75495e04f 100644
>> --- a/kernel/irq/manage.c
>> +++ b/kernel/irq/manage.c
>> @@ -723,10 +723,13 @@ EXPORT_SYMBOL(disable_irq_nosync);
>>    *     to complete before returning. If you use this function while
>>    *     holding a resource the IRQ handler may need you will
>> deadlock.
>>    *
>> - *     This function may be called - with care - from IRQ context.
>> + *     Can only be called from preemptible code as it might sleep
>> when
>> + *     an interrupt thread is associated to @irq.
>> + *
>>    */
>>   void disable_irq(unsigned int irq)
>>   {
>> +       might_sleep();
> I'm not sure about this, latest wait_event() inside synchronize_irq()
> has it already.
>
>>          if (!__disable_irq_nosync(irq))
>>                  synchronize_irq(irq);
>>   }

That is the whole point: might_sleep() should be always called. We are 
clarifying an API definition. Everyone who uses disable_irq() from 
non-sleeping context should get a warning, 100% of the time.

Not just within synchronize_irq() if there is an active threaded irq 
handler.

--

     Manfred