linux-kernel - Re: [Bug #15041] Pagemap endless read loop with LTP

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Message-Id: <201001142138.51506.rjw@sisk.pl>
Date:	Thu, 14 Jan 2010 21:38:51 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Matt Mackall <mpm@...enic.com>
Cc:	Andi Kleen <andi@...stfloor.org>,
	Américo Wang <xiyou.wangcong@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Kernel Testers List <kernel-testers@...r.kernel.org>
Subject: Re: [Bug #15041] Pagemap endless read loop with LTP

On Thursday 14 January 2010, Matt Mackall wrote:
> On Thu, 2010-01-14 at 00:50 +0100, Andi Kleen wrote:
> > On Wed, Jan 13, 2010 at 10:57:34PM +0100, Rafael J. Wysocki wrote:
> > > On Wednesday 13 January 2010, Américo Wang wrote:
> > > > On Mon, Jan 11, 2010 at 6:32 AM, Rafael J. Wysocki <rjw@...k.pl> wrote:
> > > > > This message has been generated automatically as a part of a report
> > > > > of recent regressions.
> > > > >
> > > > > The following bug entry is on the current list of known regressions
> > > > > from 2.6.32.  Please verify if it still should be listed and let me know
> > > > > (either way).
> > > > >
> > > > >
> > > > > Bug-Entry       : http://bugzilla.kernel.org/show_bug.cgi?id=15041
> > > > > Subject         : Pagemap endless read loop with LTP
> > > > > Submitter       : Andi Kleen <andi@...stfloor.org>
> > > > > Date            : 2010-01-10 2:09 (1 days old)
> > > > > References      : http://marc.info/?l=linux-kernel&m=126308941423848&w=4
> > > > >
> > > > 
> > > > According to Andi's later reply, it shoud not be an endless loop,
> > > > it just takes a rather long time.
> > > 
> > > Andi?
> > 
> > It'll try to read 47 bits worth of 0s on 64bit x86-64. 
> > 
> > I haven't tried to wait until that finishes, but I estimate a few months of 
> > CPU time at least.
> > 
> > The interface is just misdesigned, but I guess we cannot do
> > anything about that for now.
> 
> It's perfectly sensible. What's not sensible is reading the entirety of
> everything you find in /proc, something that just about every Linux
> admin figures out moments after running their first recursive grep.
> 
> >  LTP will just need to do a workaround.
> 
> Or they could actually, you know, add a test of pagemap. Not much chance
> of that, though - CVS reports it took them until 2005 to figure out that
> skipping /proc/kcore was a good idea.

Closing as "documented".

Rafael
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