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From:   Christian Eggers <ceggers@arri.de>
To:     Lars-Peter Clausen <lars@metafoo.de>
CC:     Jonathan Cameron <jic23@kernel.org>, <stable@vger.kernel.org>,
        "Hartmut Knaack" <knaack.h@gmx.de>,
        Peter Meerwald-Stadler <pmeerw@pmeerw.net>,
        <linux-iio@vger.kernel.org>, <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] iio: trigger: sysfs: Disable irqs before calling iio_trigger_poll()
Date:   Wed, 12 Aug 2020 13:01:51 +0200
Message-ID: <3847827.rc3nFVyU9p@n95hx1g2>
Organization: Arnold & Richter Cine Technik GmbH & Co. Betriebs KG
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Hi Lars

On Monday, 3 August 2020, 08:52:54 CEST, Lars-Peter Clausen wrote:
> On 8/3/20 8:44 AM, Christian Eggers wrote:
> > ...
> > is my patch sufficient, or would you prefer a different solution?
> 
> The code in normal upstream is correct, there is no need to patch it
> since iio_sysfs_trigger_work() always runs with IRQs disabled.
> 
> >> Are you using a non-upstream kernel? Maybe a RT kernel?
> > 
> > I use v5.4.<almost-latest>-rt
> 
> That explains it. Have a look at
> 0200-irqwork-push-most-work-into-softirq-context.patch.
> 
> The right fix for this issue is to add the following snippet to the RT
> patchset.
> 
> diff --git a/drivers/iio/trigger/iio-trig-sysfs.c
> b/drivers/iio/trigger/iio-trig-sysfs.c
> --- a/drivers/iio/trigger/iio-trig-sysfs.c
> +++ b/drivers/iio/trigger/iio-trig-sysfs.c
> @@ -161,6 +161,7 @@ static int iio_sysfs_trigger_probe(int id)
>       iio_trigger_set_drvdata(t->trig, t);
> 
>       init_irq_work(&t->work, iio_sysfs_trigger_work);
> +    t->work.flags = IRQ_WORK_HARD_IRQ;
> 
>       ret = iio_trigger_register(t->trig);
>       if (ret)

I can confirm that this works for iio-trig-sysfs on 5.4.54-rt32. Currently I 
do not use iio-trig-hrtimer, but if I remember correctly, the problem was also 
present there.

Do you want to apply your patch for mainline? In contrast to v5.4, 
IRQ_WORK_HARD_IRQ is already available there (moved to smp_types.h). 
Unfortunately I cannot test it on mainline for now, as my BSP stuff is not 
ported yet.

Best regards
Christian