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

Rafael J. Wysocki
2010-01-14T20:38:51Z

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, AmÃ©rico Wang wrote:
> > > > On Mon, Jan 11, 2010 at 6:32 AM, Rafael J. Wysocki <rjw-KKrjLPT3xs0@public.gmane.org> 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-Vw/NltI1exuRpAAqCnN02g@public.gmane.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