linux-kernel - Re: [PATCH] [13/16] HWPOISON: The high level memory error handler in the VM v3

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Message-ID: <20090601113933.GD5018@wotan.suse.de>
Date:	Mon, 1 Jun 2009 13:39:33 +0200
From:	Nick Piggin <npiggin@...e.de>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Russ Anderson <rja@....com>, hugh@...itas.com, riel@...hat.com,
	akpm@...ux-foundation.org, chris.mason@...cle.com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	fengguang.wu@...el.com
Subject: Re: [PATCH] [13/16] HWPOISON: The high level memory error handler in the VM v3

On Sat, May 30, 2009 at 08:42:44AM +0200, Andi Kleen wrote:
> Sorry for late answer, email slipped out earlier.
> 
> On Thu, May 28, 2009 at 11:56:25AM -0500, Russ Anderson wrote:
> > > I changed it to 
> > > 
> > >  "MCE: Unable to determine user space address during error handling\n")
> > > 
> > > Still not perfect, but hopefully better.
> > 
> > Is it even worth having a message at all?  Does the fact that page_address_in_vma()
> 
> I like having a message so that I can see when it happens.
> 
> > failed change the behavior in any way?  (Does tk->addr == 0 matter?)  From
> 
> It just doesn't report an address to the user (or rather 0)
> 
> > If the message is for developers/debugging, it would be nice to have more
> 
> It's not really for debugging only, it's a legitimate case. Typically
> when the process unmaps or remaps in parallel. Of course when it currently
> unmaps you could argue it doesn't need the data anymore and doesn't
> need to be killed (that's true), but that doesn't work for mremap()ing.
> I considered at some point to loop, but that would risk live lock.
> So it just prints and reports nothing.
> 
> The only ugly part is the ambiguity of reporting a 0 address (in theory
> there could be real memory 0 on virtual 0), but that didn't seem to be
> enough an issue to fix.

Just isn't really something we typically give a dmesg for.

Surely you can test it out these cases with debugging code or printks
and then take them out of production code?

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