Re: [RFC PATCH] iio: trigger: Fix a scheduling whilst atomic issue seen on tsc2046

[Oleksij Rempel <o.rempel@pengutronix.de>]

On Sun, Dec 05, 2021 at 05:35:35PM +0000, Jonathan Cameron wrote:
> On Wed, 24 Nov 2021 09:48:22 +0100
> Oleksij Rempel <o.rempel@pengutronix.de> wrote:
> 
> > On Sun, Oct 17, 2021 at 06:22:09PM +0100, Jonathan Cameron wrote:
> > > From: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> > > 
> > > IIO triggers are software IRQ chips that split an incoming IRQ into
> > > separate IRQs routed to all devices using the trigger.
> > > When all consumers are done then a trigger callback reenable() is
> > > called.  There are a few circumstances under which this can happen
> > > in atomic context.
> > > 
> > > 1) A single user of the trigger that calls the iio_trigger_done()
> > > function from interrupt context.
> > > 2) A race between disconnecting the last device from a trigger and
> > > the trigger itself sucessfully being disabled.
> > > 
> > > To avoid a resulting scheduling whilst atomic, close this corner
> > > by using schedule_work() to ensure the reenable is not done in atomic
> > > context.
> > > 
> > > Note that drivers must be careful to manage the interaction of
> > > set_state() and reenable() callbacks to ensure appropriate reference
> > > counting if they are relying on the same hardware controls.
> > > 
> > > Completely untested beyond building. Given it is Sunday evening
> > > very high chance of it being entirely wrong.  The potential race
> > > conditions around this were giving me a headache, but I think this
> > > is at least a step in the right direction and should work for Oleksij's
> > > case.
> > > 
> > > Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> > > Cc: Oleksij Rempel <o.rempel@pengutronix.de>
> > > Cc: Pengutronix Kernel Team <kernel@pengutronix.de>
> > > Cc: Dmitry Torokhov <dmitry.torokhov@gmail.com>  
> > 
> > Tested-by: Oleksij Rempel <o.rempel@pengutronix.de>
> > 
> > Works for me... Thank you! :)
> 
> This patch is in the category that make me nervous, so I'm 
> not going to rush it in as a fix.  I've queued it up for the next
> merge window (and marked it for Stable).  Hopefully any issues will
> shake out before it hits a release kernel.
> 
> Applied to the togreg branch of iio.git and pushed out as testing.

Thx!

> Oleksij, what do you want to do about the work around you had?
> If you think it is a good cleanup, please resend so we get it to the
> top of people's inboxes!

I'm on vacation right now. Will do it early next year.

Regards,
Oleksij
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