linux-kernel - Re: [PATCH v2 01/15] genirq/devres: Add error information printing for devm_request_threaded

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Date:   Mon, 3 Jul 2023 14:28:25 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Yangtao Li <frank.li@...o.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
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Subject: Re: [PATCH v2 01/15] genirq/devres: Add error information printing
 for devm_request_threaded_irq()

On 03/07/2023 13:54, Yangtao Li wrote:
> Hi Krzysztof,
> 
> On 2023/6/30 19:11, Thomas Gleixner wrote:
>> On Tue, Jun 27 2023 at 13:00, Uwe Kleine-König wrote:
>>> On Tue, Jun 27, 2023 at 06:12:01PM +0800, Yangtao Li wrote:
>>>
>>> While I assume changing to dev_err_probe is a result of my concern that
>>> no error should be printed when rc=-EPROBEDEFER, my other concern that
>>> adding an error message to a generic allocation function is a bad idea
>>> still stands.
>> I agree in general, but if you actually look at the call sites of
>> devm_request_threaded_irq() then the vast majority of them print more or
>> less lousy error messages. A quick grep/sed/awk/sort/uniq revealed
>>
>>       519 messages total (there are probably more)
>>
>>       352 unique messages
>>
>>       323 unique messages after lower casing
>>
>>           Those 323 are mostly just variants of the same patterns with slight
>>           modifications in formatting and information provided.
>>
>>       186 of these messages do not deliver any useful information,
>>           e.g. "no irq", "
>>
>>       The most useful one of all is: "could request wakeup irq: %d"
>>
>> So there is certainly an argument to be made that this particular
>> function should print a well formatted and informative error message.
>>
>> It's not a general allocator like kmalloc(). It's specialized and in the
>> vast majority of cases failing to request the interrupt causes the
>> device probe to fail. So having proper and consistent information why
>> the device cannot be used _is_ useful.
>>
>> Yangtao: The way how this is attempted is not useful at all.
>>
>>      1) The changelog is word salad and provides 0 rationale
>>
>>         Also such series require a cover letter...
>>
>>      2) The dev_err() which is added is not informative at all and cannot
>>         replace actually useful error messages. It's not that hard to
>>         make it useful.
>>
>>      2) Adding the printks unconditionally first will emit two messages
>>         with different content.
>>
>>         This is not how such changes are done.
>>
>>         The proper approach is to create a wrapper function which emits
>>         the error message:
>>
>>         wrapper(....., const char *info)
>>         {
>>              ret = devm_request_threaded_irq(....);
>>              if (ret < 0) {
>>                 dev_err(dev, "Failed to request %sinterrupt %u %s %s: %d\n,
>>                         thread_fn ? "threaded " : "",
>>                         irq, devname, info ? : "", ret);
>>              }
>>              return ret;
>>         }
> 
> 
> Here.
> 
> V3 was modified according to tglx's suggestion, if there is any problem, 
> please point out.

The comment was about request_thread_irq, not about devres alloc. Don't
mix the places. Really, since when do we print any errors on ENOMEM?

Best regards,
Krzysztof