linux-kernel - Re: [PATCH] genirq/devres: Simplify API devm_free

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Message-ID: <87sest94ag.ffs@tglx>
Date: Fri, 18 Oct 2024 10:57:43 +0200
From: Thomas Gleixner <tglx@...utronix.de>
To: Zijun Hu <zijun_hu@...oud.com>
Cc: linux-kernel@...r.kernel.org, Zijun Hu <quic_zijuhu@...cinc.com>
Subject: Re: [PATCH] genirq/devres: Simplify API devm_free_irq() implementation

On Fri, Oct 18 2024 at 06:36, Zijun Hu wrote:
> On 2024/10/18 04:33, Thomas Gleixner wrote:
>>> It is simpler if devm_free_irq() is undoing what any devm_request_irq()
>>> variant did, otherwise, it can avoid wrong and undesired free_irq().
>> 
>> This is confusing at best. What's the wrong an undesired free_irq()?
>> 
> for current devm_free_irq(..., irq_A, ...):
> it is undesired if irq_A is requested by request_irq().
> it is wrong and dangerous if irq_A was never requested.

There is nothing dangerous about it if it was never requested.
free_irq() won't find a irq action which matches devid and do nothing
than emitting a warning.

But that's not relevant either because there is no matching devres entry
when the interrupt was not requested via devres_request_irq(), so
free_irq() will not be reached because devres_destroy() will return
-ENOENT.

So all this change does is changing the logic from:

devres_free_irq()
    if (devres_destroy())
        return;
    free_irq();

to
    devres_release()

where devres_release() does the same thing as the above, i.e. it looks
up the devres for a match and if found, it removes and frees the devres
pointer and invokes the release function which in turn invokes
free_irq().

So in terms of code logic this is exactly the same and does neither
avoid or prevent anything.

All it does is sparing a single line of code.

Thanks,

        tglx