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 21:27:35 +0200
From:   Juergen Gross <jgross@...e.com>
To:     Joe Perches <joe@...ches.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 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@...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...");

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