Re: [PATCH 02/15] iio: trigger: fail the attach if no sub-IRQ is left

[Jonathan Cameron <jic23@kernel.org>]

On Wed, 28 Oct 2026 09:38:57 +0000
Nuno Sá <nuno.sa@analog.com> wrote:

> On Tue, Oct 27, 2026 at 05:19:06PM +0100, Greg Kroah-Hartman wrote:
> > From: Josef Bacik <josef@toxicpanda.com>
> > 
> > A trigger can serve CONFIG_IIO_CONSUMERS_PER_TRIGGER devices, two by
> > default.  When one more device is attached, iio_trigger_get_irq() returns
> > -ENOMEM.  iio_trigger_attach_poll_func() prints an error, drops the module
> > reference and jumps to its exit, but ret is still 0 there, so it reports
> > success.
> > 
> > iio_enable_buffers() goes on as if the poll function were attached.  The
> > write to buffer/enable succeeds, but no sample ever arrives.  When the
> > buffer is disabled again, iio_trigger_detach_poll_func() undoes an attach
> > which has not taken place, with -ENOMEM in pf->irq:
> > 
> >  - iio_trigger_put_irq() calls clear_bit() with the bit number
> >    -ENOMEM - trig->subirq_base, which clears a bit in whatever lies in
> >    front of trig->pool;
> >  - if only one of the real consumers is left, the trigger is switched off
> >    under it;
> >  - module_put() drops a reference to the driver module which has been
> >    dropped already.
> > 
> > All it takes is to set the same trigger as current_trigger of three
> > devices and to enable their buffers.
> > 
> > Return the error.
> > 
> > Fixes: 995438233579 ("iio: Fix error handling in iio_trigger_attach_poll_func")
> > Cc: stable <stable@kernel.org>
> > Cc: David Lechner <dlechner@baylibre.com>
> > Cc: "Nuno Sá" <nuno.sa@analog.com>
> > Cc: Andy Shevchenko <andy@kernel.org>
> > Cc: Leonard Crestez <cdleonard@gmail.com>
> > Signed-off-by: Josef Bacik <josef@toxicpanda.com>
> > Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> > ---  
> 
> Reviewed-by: Nuno Sá <nuno.sa@analog.com>
> 
Another one where it seems the LLMs are feeding the same to multiple
people. 
Currently on my fixes-togreg tree is:
ef017c440534 ("iio: trigger: Return an error when the trigger has no free irq")
From Karl Mehltretter

> >  drivers/iio/industrialio-trigger.c | 1 +
> >  1 file changed, 1 insertion(+)
> > 
> > diff --git a/drivers/iio/industrialio-trigger.c b/drivers/iio/industrialio-trigger.c
> > index 76926fee0f84..fc4651490d42 100644
> > --- a/drivers/iio/industrialio-trigger.c
> > +++ b/drivers/iio/industrialio-trigger.c
> > @@ -293,6 +293,7 @@ int iio_trigger_attach_poll_func(struct iio_trigger *trig,
> >  	if (pf->irq < 0) {
> >  		pr_err("Could not find an available irq for trigger %s, CONFIG_IIO_CONSUMERS_PER_TRIGGER=%d limit might be exceeded\n",
> >  			trig->name, CONFIG_IIO_CONSUMERS_PER_TRIGGER);
> > +		ret = pf->irq;
> >  		goto out_put_module;
> >  	}
> >  
> > 
> > -- 
> > 2.56.0
> >