linux-kernel - Re: [PATCH RT 1/1] remoteproc: Prevent schedule while atomic

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Date:   Tue, 28 Mar 2017 10:31:56 +0100
From:   Lee Jones <lee.jones@...aro.org>
To:     Julia Cartwright <julia@...com>
Cc:     Lionel DEBIEVE <lionel.debieve@...com>,
        Grygorii Strashko <grygorii.strashko@...com>,
        Steven Rostedt <rostedt@...dmis.org>,
        "linux-rt-users@...r.kernel.org" <linux-rt-users@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "bigeasy@...utronix.de" <bigeasy@...utronix.de>,
        "tglx@...utronix.de" <tglx@...utronix.de>
Subject: Re: [PATCH RT 1/1] remoteproc: Prevent schedule while atomic

On Thu, 23 Mar 2017, Julia Cartwright wrote:

> On Thu, Mar 23, 2017 at 10:26:49AM +0000, Lee Jones wrote:
> > On Thu, 23 Mar 2017, Lionel DEBIEVE wrote:
> > 
> > > On 03/22/2017 07:47 PM, Julia Cartwright wrote:
> > > > On Wed, Mar 22, 2017 at 01:30:12PM -0500, Grygorii Strashko wrote:
> > > >> On 03/22/2017 01:01 PM, Steven Rostedt wrote:
> > > >>> On Wed, 22 Mar 2017 12:37:59 -0500
> > > >>> Julia Cartwright <julia@...com> wrote:
> > > >>>
> > > >>>> Which kernel were you testing on, here?  From what I can tell, this
> > > >>>> should have been fixed with Thomas's commit:
> > > >>>>
> > > >>>>     2a1d3ab8986d ("genirq: Handle force threading of irqs with primary
> > > >>>> and thread handler")
> > > >>> Thanks Julia for looking into this. I just looked at the code, and saw
> > > >>> that it does very little with the lock held, and was fine with the
> > > >>> conversion. But if that interrupt handler should be in a thread, we
> > > >>> should see if that's the issue first.
> > > >>
> > > >> It will not be threaded because there are IRQF_ONESHOT used.
> > > >>
> > > >> 	ret = devm_request_threaded_irq(&pdev->dev, irq,
> > > >> 					sti_mbox_irq_handler,
> > > >> 					sti_mbox_thread_handler,
> > > >> 					IRQF_ONESHOT, mdev->name, mdev);
> > > > Indeed.  I had skipped over this important detail when I was skimming
> > > > through the code.
> > > >
> > > > Thanks for clarifying!
> > > >
> > > > Is IRQF_ONESHOT really necessary for this device?  The primary handler
> > > > invokes sti_mbox_disable_channel() on the interrupting channel, which I
> > > > would hope would acquiesce the pending interrupt at the device-level?
> > 
> > Not sure.  This part of the code is remanent from when I re-wrote it.
> > 
> > What is the alternative?
> 
> If, on the completed execution of the registered primary handler, you
> can ensure that the device is no longer asserting an interrupt to the
> connected irq chip, then the IRQF_ONESHOT isn't necessary, because it's
> safe for the irq core to unmask the interrupt after the primary handler
> runs.
> 
> It appears that it might be able to make this guarantee, if that's what
> sti_mbox_disable_channel() is doing.

Yes, I'm inclined to agree.

> > NB: What does 'acquiesce' mean in this context?  Is that a typo?
> 
> I mean 'acquiesce' to mean what I mention before: prevent the device
> from asserting the interrupt.  Perhaps it's a uncommon use of the word.

http://www.thesaurus.com/browse/acquiesce

Perhaps 'suppress' or 'quell' would better suit the situation.

-- 
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
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