From: Jeff Dike <jdike@addtoit.com>
To: Graham Cobb <g+debian@cobb.uk.net>
Cc: Mattia Dongili <malattia@linux.it>,
495611@bugs.debian.org,
UML-devel <user-mode-linux-devel@lists.sourceforge.net>
Subject: Re: [uml-devel] [Pkg-uml-pkgs] Bug#495611: user-mode-linux: page_mapcount(page) went negative!
Date: Wed, 3 Sep 2008 13:21:52 -0400 [thread overview]
Message-ID: <20080903172152.GB8769@c2.user-mode-linux.org> (raw)
In-Reply-To: <200809030001.20439.g+debian@cobb.uk.net>
On Wed, Sep 03, 2008 at 12:01:19AM +0100, Graham Cobb wrote:
> The bisection is complete. It took longer than I expected as many of the
> versions git-bisect wanted to test would not build UML without tracking down
> some additional patches.
>
> The bug seems to have been introduced with git commit
> 3963333fe6767f15141ab2dc3b933721c636c212 (uml: cover stubs with a VMA).
Excellent, the backtrace now makes a bit of sense. It looks like the
VMAs at the top of the address space are being overmapped by a call to
mmap. The question is why does it look like there's a big enough hole
there, when it ends up unmapping the stubs in order to make room for
the mmap.
> With hindsight I suppose I could have guessed that would be the commit: the
> crash seemed to be when unmapping a VMA. If my reading of the page flags is
> correct the problem is that the page has the PG_reserved flag set, so what is
> it doing in the VMA which is being unmapped?
A page of kernel code is mapped into the process. This page (and all
other pages containing kernel text) is marked reserved during boot.
> Let me know if you want me to run some more tests, for example if you want to
> add some printk's in the code to understand more about what is going on.
I'm going to need some more information. I'll get back to you with a
patch...
Jeff
--
Work email - jdike at linux dot intel dot com
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prev parent reply other threads:[~2008-09-03 17:22 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20080818230509.23819.90290.reportbug@carrera.home.cobb.me.uk>
2008-08-19 12:01 ` [uml-devel] [Pkg-uml-pkgs] Bug#495611: user-mode-linux: page_mapcount(page) went negative! Mattia Dongili
2008-08-26 20:22 ` Jeff Dike
[not found] ` <200808271605.25584.graham@cobb.uk.net>
2008-08-27 17:13 ` Jeff Dike
2008-09-02 23:01 ` Graham Cobb
2008-09-03 17:21 ` Jeff Dike [this message]
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