Re: Xen /dev/mcelog registration in Linux

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Tue, Dec 15, 2015 at 02:54:31PM +0100, Marek Marczykowski-Górecki wrote:
> Hi,
> 
> Booting kernel with both CONFIG_X86_MCE=y and CONFIG_XEN_MCE_LOG=y
> 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-Górecki
> 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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