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

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Date:	Fri, 18 Nov 2011 14:00:44 +0000
From:	Ian Campbell <Ian.Campbell@...rix.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	ANNIE LI <annie.li@...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 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).

Ian.



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