linux-kernel - Re: [PATCH 3/4] media: dw100: Fix kernel oops with PREEMPT

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Message-ID: <8a8ec84e5484d7a1a5e6fac9a5238f3cae66abc3.camel@ndufresne.ca>
Date: Mon, 05 Jan 2026 14:02:38 -0500
From: Nicolas Dufresne <nicolas@...fresne.ca>
To: Stefan Klug <stefan.klug@...asonboard.com>, Xavier Roumegue	
 <xavier.roumegue@....nxp.com>, Mauro Carvalho Chehab <mchehab@...nel.org>, 
 Sebastian Andrzej Siewior	 <bigeasy@...utronix.de>, Clark Williams
 <clrkwllms@...nel.org>, Steven Rostedt	 <rostedt@...dmis.org>, Laurent
 Pinchart <laurent.pinchart@...asonboard.com>
Cc: linux-media@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-rt-devel@...ts.linux.dev
Subject: Re: [PATCH 3/4] media: dw100: Fix kernel oops with PREEMPT_RT
 enabled

Hi,

Le lundi 05 janvier 2026 à 12:35 +0100, Stefan Klug a écrit :
> On kernels with PREEMPT_RT enabled, a "BUG: scheduling while atomic"
> kernel oops occurs inside dw100_irq_handler -> vb2_buffer_done. This is
> because vb2_buffer_done takes a spinlock which is not allowed within
> interrupt context on PREEMPT_RT.
> 
> Fix that by making the irq handler threaded. The threaded interrupt
> handling might cause the interrupt line to be disabled a little longer
> than before. As the line is not shared, this has no negative side
> effects.

That's interesting, do you plan to update more drivers ? There is a lot of m2m
using hard IRQ to minimize the idle time (save a context switch), but RT support
might be more worth then that.

> 
> Signed-off-by: Stefan Klug <stefan.klug@...asonboard.com>

Reviewed-by: Nicolas Dufresne <nicolas.dufresne@...labora.com>

> ---
>  drivers/media/platform/nxp/dw100/dw100.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/media/platform/nxp/dw100/dw100.c
> b/drivers/media/platform/nxp/dw100/dw100.c
> index
> 8a421059a1c9b55f514a29d3c2c5a6ffb76e0a64..4f5ef70e5f4a052fb5f208e35f8785f9d30d
> c54e 100644
> --- a/drivers/media/platform/nxp/dw100/dw100.c
> +++ b/drivers/media/platform/nxp/dw100/dw100.c
> @@ -1600,8 +1600,9 @@ static int dw100_probe(struct platform_device *pdev)
>  
>  	pm_runtime_put_sync(&pdev->dev);
>  
> -	ret = devm_request_irq(&pdev->dev, irq, dw100_irq_handler,
> IRQF_ONESHOT,
> -			       dev_name(&pdev->dev), dw_dev);
> +	ret = devm_request_threaded_irq(&pdev->dev, irq, NULL,
> +					dw100_irq_handler, IRQF_ONESHOT,
> +					dev_name(&pdev->dev), dw_dev);
>  	if (ret < 0) {
>  		dev_err(&pdev->dev, "Failed to request irq: %d\n", ret);
>  		goto err_pm;

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