Re: [PATCH] Revert "uio: use threaded interrupts"

[Chris Packham]

Hi Mike,

On 06/11/2026 12:22, Mike Schanne wrote:
> This reverts commit f8a27dfa4b82d442af1c0645a5acc70cc97c67f6.
>
> The original solution breaks the threadirqs case including PREEMPT_RT
> Under PREEMPT_RT, it adds an extra kthread per UIO irq,
> which adds a context switch per interrupt.
>
> See:
> https://lore.kernel.org/all/20240326195927.3265297-1-chris.packham@xxxxxxxxxxxxxxxxxxx/
> https://github.com/torvalds/linux/commit/f8a27dfa4b82d442af1c0645a5acc70cc97c67f6
>
> Signed-off-by: Michael Schanne <mschanne@xxxxxxx>
Acked-by: Chris Packham <chris.packham@xxxxxxxxxxxxxxxxxxx>

I'll have to dig out the board that had the original problem and look 
for a different fix.

> ---
>   drivers/uio/uio.c | 19 +++++--------------
>   1 file changed, 5 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/uio/uio.c b/drivers/uio/uio.c
> index f8fa20522660..9ef5b276b090 100644
> --- a/drivers/uio/uio.c
> +++ b/drivers/uio/uio.c
> @@ -442,30 +442,21 @@ EXPORT_SYMBOL_GPL(uio_event_notify);
>    * @irq: IRQ number, can be UIO_IRQ_CYCLIC for cyclic timer
>    * @dev_id: Pointer to the devices uio_device structure
>    */
> -static irqreturn_t uio_interrupt_handler(int irq, void *dev_id)
> +static irqreturn_t uio_interrupt(int irq, void *dev_id)
>   {
>          struct uio_device *idev = (struct uio_device *)dev_id;
>          irqreturn_t ret;
>
>          ret = idev->info->handler(irq, idev->info);
>          if (ret == IRQ_HANDLED)
> -               ret = IRQ_WAKE_THREAD;
> -
> -       return ret;
> -}
> -
>   /**
>    * uio_interrupt_thread - irq thread handler
>    * @irq: IRQ number
>    * @dev_id: Pointer to the devices uio_device structure
>    */
> -static irqreturn_t uio_interrupt_thread(int irq, void *dev_id)
> -{
> -       struct uio_device *idev = (struct uio_device *)dev_id;
> +               uio_event_notify(idev->info);
>
> -       uio_event_notify(idev->info);
> -
> -       return IRQ_HANDLED;
> +       return ret;
>   }
>
>   struct uio_listener {
> @@ -1044,8 +1035,8 @@ int __uio_register_device(struct module *owner,
>                   * FDs at the time of unregister and therefore may not be
>                   * freed until they are released.
>                   */
> -               ret = request_threaded_irq(info->irq, uio_interrupt_handler, uio_interrupt_thread,
> -                                          info->irq_flags, info->name, idev);
> +               ret = request_irq(info->irq, uio_interrupt,
> +                                 info->irq_flags, info->name, idev);
>                  if (ret) {
>                          info->uio_dev = NULL;
>                          goto err_request_irq;
> --
> 2.53.0
>
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