linux-kernel - Re: [PATCH v2] xen/mce: don't issue error message for failed /dev/mcelog registration

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Date:   Tue, 13 Jun 2017 09:31:54 -0700
From:   Joe Perches <joe@...ches.com>
To:     Juergen Gross <jgross@...e.com>, Ingo Molnar <mingo@...nel.org>
Cc:     linux-kernel@...r.kernel.org, xen-devel@...ts.xenproject.org,
        x86@...nel.org, boris.ostrovsky@...cle.com, hpa@...or.com,
        tglx@...utronix.de, mingo@...hat.com, tony.luck@...el.com,
        bp@...en8.de
Subject: Re: [PATCH v2] xen/mce: don't issue error message for failed
 /dev/mcelog registration

On Tue, 2017-06-13 at 18:13 +0200, Juergen Gross wrote:
> On 13/06/17 17:20, Ingo Molnar wrote:
> > * Juergen Gross <jgross@...e.com> wrote:
> > 
> > > When running under Xen as dom0 /dev/mcelog is being registered by Xen
> > > instead of the normal mcelog driver. Avoid an error message being
> > > issued by the mcelog driver in this case. Instead issue an informative
> > > message that Xen has registered the device.
[]
> > > diff --git a/arch/x86/kernel/cpu/mcheck/dev-mcelog.c b/arch/x86/kernel/cpu/mcheck/dev-mcelog.c
[]
> > > @@ -388,9 +388,16 @@ static __init int dev_mcelog_init_device(void)
> > >  	/* register character device /dev/mcelog */
> > >  	err = misc_register(&mce_chrdev_device);
> > >  	if (err) {
> > > -		pr_err("Unable to init device /dev/mcelog (rc: %d)\n", err);
> > > -		return err;
> > > +		if (err == -EBUSY)
> > > +			/* Xen dom0 might have registered the device already. */
> > > +			pr_info("Unable to init device /dev/mcelog, already registered");
> > > +		else {
> > > +			pr_err("Unable to init device /dev/mcelog (rc: %d)\n",
> > > +			       err);
> > > +			return err;
> > > +		}
> > 
> > Please only use balanced curly braces in conditional statements.
> 
> Okay, will change.

Perhaps better is to reverse the test

		if (err != -EBUSY) {
			pr_err("Unable to ....", err);
			return err;
		}
		pr_info("etc...");

		[ rest of code at this indentation ]

but it looks like you added a logic defect too and
this code should be:

	if (err) {
		if (err == -EBUSY)
			pr_info(...)
		else
			pr_err(...)
		return err;
	}

or less indented using

	err = misc_register(&mce_chrdev_device);
	if (err == -EBUSY) {
		pr_info(...);
		return err;
	} else if (err) {
		pr_err(...);
		return err;
	}