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    SubjectRe: [PATCH v2] xen/mce: don't issue error message for failed /dev/mcelog registration
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    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@suse.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.

    You should definitely mention that behavior change
    in the changelog.

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