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

[Juergen Gross <jgross@xxxxxxxx>]

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.


Juergen

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