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

[Joe Perches <joe@xxxxxxxxxxx>]

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...");

                [ 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;
        }


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