From mboxrd@z Thu Jan  1 00:00:00 1970
From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Subject: Re: Xen /dev/mcelog registration in Linux
Date: Mon, 4 Jan 2016 15:49:11 -0500
Message-ID: <20160104204911.GD17427@char.us.oracle.com>
References: <20151215135431.GQ16649@mail-itl>
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To: Marek =?iso-8859-1?Q?Marczykowski-G=F3recki?= <marmarek@invisiblethingslab.com>
Cc: xen-devel <xen-devel@lists.xen.org>
List-Id: xen-devel@lists.xenproject.org

On Tue, Dec 15, 2015 at 02:54:31PM +0100, Marek Marczykowski-G=F3recki wrot=
e:
> Hi,
> =

> Booting kernel with both CONFIG_X86_MCE=3Dy and CONFIG_XEN_MCE_LOG=3Dy
> results in "mce: Unable to init device /dev/mcelog (rc: -16)" error. I
> think that's because both drivers tries to register that character
> device (drivers/xen/mcelog.c: xen_late_init_mcelog;
> arch/x86/kernel/cpu/mcheck/mce.c: mcheck_init_device). So obviously one
> of them fails. CONFIG_XEN_MCE_LOG depends on CONFIG_X86_MCE...
>

Right. The baremetal one (mce.c) should fail and then the Xen one
will pick it up. There is a little comment in threshold_init_device:


/*                                                                         =
     =

 * there are 3 funcs which need to be _initcalled in a logic sequence:     =
     =

 * 1. xen_late_init_mcelog                                                 =
     =

 * 2. mcheck_init_device                                                   =
     =

 * 3. threshold_init_device                                                =
     =

 *                                                                         =
     =

 * xen_late_init_mcelog must register xen_mce_chrdev_device before         =
     =

 * native mce_chrdev_device registration if running under xen platform;    =
     =

 *                                                                         =
     =

 * mcheck_init_device should be inited before threshold_init_device to     =
     =

 * initialize mce_device, otherwise a NULL ptr dereference will cause panic=
.       =

 *                                                                         =
     =

 * so we use following _initcalls                                          =
     =

 * 1. device_initcall(xen_late_init_mcelog);                               =
     =

 * 2. device_initcall_sync(mcheck_init_device);                            =
     =

 * 3. late_initcall(threshold_init_device);                                =
     =

 *                                                                         =
     =

 * when running under xen, the initcall order is 1,2,3;                    =
     =

 * on baremetal, we skip 1 and we do only 2 and 3.                         =
     =

 */                                                                   =

 =

> How is that supposed to work?

Hope the above explains it?
> =

> -- =

> Best Regards,
> Marek Marczykowski-G=F3recki
> Invisible Things Lab
> A: Because it messes up the order in which people normally read text.
> Q: Why is top-posting such a bad thing?



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