linux-kernel - RE: [PATCH 1/3] xen/mce: Add mcelog support for Xen platform (RFC)

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Message-ID: <DE8DF0795D48FD4CA783C40EC82923351FC523@SHSMSX101.ccr.corp.intel.com>
Date:	Wed, 30 May 2012 15:20:03 +0000
From:	"Liu, Jinsong" <jinsong.liu@...el.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	Borislav Petkov <bp@...64.org>,
	"'linux-kernel@...r.kernel.org'" <linux-kernel@...r.kernel.org>,
	"Luck, Tony" <tony.luck@...el.com>,
	"'xen-devel@...ts.xensource.com'" <xen-devel@...ts.xensource.com>
Subject: RE: [PATCH 1/3] xen/mce: Add mcelog support for Xen platform (RFC)

Konrad Rzeszutek Wilk wrote:
> On Wed, May 30, 2012 at 03:09:12PM +0000, Liu, Jinsong wrote:
>>> 
>>> Still no go, this is current linus with your patch applied. I'll
>>> look into it later when there's time.
>> 
>> The root cause is,
>> 1). at cpu/mcheck/mce.c, device_initcall_sync(mcheck_init_device) is
>> *after* all device_initcall(); 2). at cpu/mcheck/mce_amd.c,
>> device_initcall(threshold_init_device) will    
>> threshold_init_device  
>>     --> threshold_create_device
>>     --> threshold_create_bank
>>     --> kobject_create_and_add(name, &dev->kobj);
>>         // at this point, struct device *dev = per_cpu(mce_device,
>>         cpu), which is a NULL pointer. // mce_device is initialized
>> at mcheck_init_device --> mce_device_create 3). so kernel panic 
>> 
>> So our RFC patch would affect amd mce logic.
>> 
>> ===========================
>> 
>> I have a thought about symlink approach, but seems it would bring
>> more issues, e.g. 1). it need change more native mce code, like
>> remove /dev/mcelog which created at native mce (under xen platform),
>> or 2). it still need to change device_initcall(mcheck_init_device)
>> to device_initcall_sync(mcheck_init_device), if it want to
>> implicitly block native /dev/mcelog --> but that would panic amd mce
>> logic.    
>> 
>> IMO currently there are 2 options:
>> 1). use the original approach (implicitly redirect /dev/mcelog to
>> xen_mce_chrdev_device) --> what point of this approach do you think
>> unreasonable? It just remove a 'static' from native mce code! 2).
>> use another /dev/xen-mcelog interface, with another misc minor '226'
> 
> The 2) is no good.
> 
> 3) What about moving the corresponding other users (so
> threshold_init_device), to be at late_initcall and the mce to be at
> late_initcall_sync 

I can try, but only if Boris would not jump out.
and it can only be tested by Boris at AMD platform :(

> 
> 4) Or make the driver you are making start at fs_initcall ?

It's risky, I'm not sure whether dd ready at that time point, but I can have a look at it.

Thanks,
Jinsong

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