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

[Joe Perches]

On Tue, 2017-06-13 at 21:27 +0200, Juergen Gross wrote:
> On 13/06/17 18:31, Joe Perches wrote:
> > On Tue, 2017-06-13 at 18:13 +0200, Juergen Gross wrote:
> > > On 13/06/17 17:20, Ingo Molnar wrote:
> > > > * Juergen Gross <jgross@xxxxxxxx> 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...");
> 
> Okay.
> 
> > 
> > 		[ 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;
> > 	}
> 
> I didn't want to omit the call to mce_register_decode_chain() in the Xen
> case.

You should definitely mention that behavior change
in the changelog.