linux-kernel - Re: irqdesc: Why the "__ref" is needed in __irq_alloc

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Message-ID: <alpine.DEB.2.21.1803091237320.1364@nanos.tec.linutronix.de>
Date:   Fri, 9 Mar 2018 12:39:53 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Dou Liyang <douly.fnst@...fujitsu.com>
cc:     Kees Cook <keescook@...omium.org>, re.emese@...il.com,
        Marc Zyngier <marc.zyngier@....com>,
        linux-kernel@...r.kernel.org
Subject: Re: irqdesc: Why the "__ref" is needed in __irq_alloc_descs() ?

On Fri, 9 Mar 2018, Dou Liyang wrote:
> I have a question about "__ref" in Linux kernel.
> 
> When I looked into the __irq_alloc_descs(), I found it tagged a
> "__ref" mark, but I didn't find that it referenced code or data
> from init section.

See the various

#define irq_alloc_desc* 

variants. That will give you enough use cases from init.

> And after I tested, seems "__ref" just puts the code into a different
> section that is not checked by modpost. It does not affect the
> performance whether it is tagged or not. Is it right?

Well having code in a different section can cause performance issues, but
that only matters in a hotpath. irq_alloc_desc* is not performance critical
at all, so nothing to worry about.

Thanks,

	tglx