linux-kernel - Re: [RFC PATCH] notifier: Return non-null when callback already registered

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Message-ID: <YKe+ckYQHebPYLBD@zn.tnic>
Date:   Fri, 21 May 2021 16:06:42 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     X86 ML <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] notifier: Return non-null when callback already
 registered

On Fri, May 21, 2021 at 01:11:42PM +0200, Peter Zijlstra wrote:
> > @@ -25,7 +25,7 @@ static int notifier_chain_register(struct notifier_block **nl,
> >  	while ((*nl) != NULL) {
> >  		if (unlikely((*nl) == n)) {
> >  			WARN(1, "double register detected");
> 
> That should give a big clue^

Yah, the big cluebat... Was wondering whether to remove it, actually.
But then I'd need to audit all users whether they handle retval
properly. Sounds like a kernelnewbies project to me...

> > -			return 0;
> > +			return 1;
> 
> How about -EBUSY here?

Yah, anthing but 0.

But if we're gonna return -E things, -EEXIST looks like an even better
fit to me...

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette