linux-kernel - Re: [PATCH 01/15] genirq/devres: Add error information printing for devm_request_threaded

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Date:   Tue, 27 Jun 2023 10:49:48 +0200
From:   Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To:     Yangtao Li <frank.li@...o.com>
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Subject: Re: [PATCH 01/15] genirq/devres: Add error information printing for
 devm_request_threaded_irq()

Hello,

On Tue, Jun 27, 2023 at 03:16:52PM +0800, Yangtao Li wrote:
> Ensure that all error handling branches print error information. In this
> way, when this function fails, the upper-layer functions can directly
> return an error code without missing debugging information. Otherwise,
> the error message will be printed redundantly or missing.
> 
> There are more than 700 calls to the devm_request_threaded_irq method.
> If error messages are printed everywhere, more than 1000 lines of code
> can be saved by removing the msg in the driver.
> 
> Signed-off-by: Yangtao Li <frank.li@...o.com>
> ---
>  kernel/irq/devres.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/irq/devres.c b/kernel/irq/devres.c
> index f6e5515ee077..94039a915218 100644
> --- a/kernel/irq/devres.c
> +++ b/kernel/irq/devres.c
> @@ -58,8 +58,10 @@ int devm_request_threaded_irq(struct device *dev, unsigned int irq,
>  
>  	dr = devres_alloc(devm_irq_release, sizeof(struct irq_devres),
>  			  GFP_KERNEL);
> -	if (!dr)
> +	if (!dr) {
> +		dev_err(dev, "Failed to allocate device resource data\n");
>  		return -ENOMEM;
> +	}
>  
>  	if (!devname)
>  		devname = dev_name(dev);
> @@ -67,6 +69,7 @@ int devm_request_threaded_irq(struct device *dev, unsigned int irq,
>  	rc = request_threaded_irq(irq, handler, thread_fn, irqflags, devname,
>  				  dev_id);
>  	if (rc) {
> +		dev_err(dev, "Failed to request threaded irq\n");
>  		devres_free(dr);
>  		return rc;
>  	}

My personal opinion is that generic allocation functions should be
silent. The reason is that the consuming driver is in a better position
to emit a helpful error message.

While there is some room to improvment in this generic variant (by
mentioning the error code and maybe also the irq number), consider a
device that has up to 3 irqs and sometimes only 1. So the driver might
want to handle some irq requesting silently. And also for non-optional
irqs

	mybus:mydev: Failed to request TX irq (EBUSY)

is much more helpful than

	mybus:mydev: Failed to request threaded irq

(Hint: "threaded" is not a helpful information here either.)

Yes, a message in the driver has the downside of making the kernel image
(or module) bigger, but the added value is IMHO worth that.

Also you might want to handle -EPROBE_DEFER and not emit a message then?
(Not sure if request_threaded_irq can return that.)

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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