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

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Message-ID: <20170322184733.GL10423@jcartwri.amer.corp.natinst.com>
Date:   Wed, 22 Mar 2017 13:47:33 -0500
From:   Julia Cartwright <julia@...com>
To:     Grygorii Strashko <grygorii.strashko@...com>
CC:     Steven Rostedt <rostedt@...dmis.org>,
        Lionel Debieve <lionel.debieve@...com>,
        <linux-rt-users@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <bigeasy@...utronix.de>, <tglx@...utronix.de>
Subject: Re: [PATCH RT 1/1] remoteproc: Prevent schedule while atomic

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?

Also, as written there are num_inst reads of STI_IRQ_VAL_OFFSET in the
primary handler, which seems inefficient...(unless of course reading
incurs side effects, here).

   Julia

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