linux-kernel - Re: [Xen-devel] Re: [PATCH 2/3] xen/granttable: Grant tables V2 implementation

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Date:	Sat, 19 Nov 2011 00:10:39 +0800
From:	annie li <annie.li@...cle.com>
To:	Ian Campbell <Ian.Campbell@...rix.com>
CC:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	"jeremy@...p.org" <jeremy@...p.org>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"kurt.hackel@...cle.com" <kurt.hackel@...cle.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Paul Durrant <Paul.Durrant@...rix.com>
Subject: Re: [Xen-devel] Re: [PATCH 2/3] xen/granttable: Grant tables V2 implementation



On 2011-11-18 22:00, Ian Campbell wrote:
> On Fri, 2011-11-18 at 13:52 +0000, Konrad Rzeszutek Wilk wrote:
>   
>>>> +                       xen_raw_printk(str);
>>>> +                       panic(str);
>>>>         
>>> I expect you've just copied this style from elsewhere but I really
>>> dislike this duplication of prints. If panic is not useful here we
>>> really ought to address that at the root instead of going around
>>> patching things to print every panic message twice. I thought
>>> earlyprintk was supposed to solve this problem. Perhaps a generic
>>> early_panic_print could be added to the panic code?
>>>       
>> We are using this combo in swiotlb-xen and as well in the xen pci.
>> We could declere a 'xen_raw_panic' that would do the job?
>>
>> The problem is that panic() uses the "late" printk mechanism (so
>> it goes through the buffer that ends up not beign flushed) and the
>> panic never sees the light.
>>     
>
> So lets fix that instead of working around it...
>
>   
>>  The 'xen_raw_printk' is synchronous..
>>
>> But I wonder if the panic surfaces if 'earlyprintk=xen' is used?
>> At which point it might be that the those extra xen_raw_printk
>> become pointless?
>>     
>
> I think panic's do come out with earlyprintk (unless they are truly
> super early).
>   
So we have two candidates:
xen_raw_printk + panic
panic + earlyprintk=xen

If panic does work with earlyprintk, then the latter one is better. 
Otherwise, there will be duplicated string printed out with 
'earlyprintk=xen'.

Thanks
Annie
> Ian.
>
>
>
>   
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