linux-kernel - Re: [PATCH] procfs task exe symlink

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Message-ID: <8bd0f97a0802192002o3446901dh9140dd166af0f1e@mail.gmail.com>
Date:	Tue, 19 Feb 2008 23:02:35 -0500
From:	"Mike Frysinger" <vapier.adi@...il.com>
To:	"Matt Helsley" <matthltc@...ibm.com>
Cc:	"Andrew Morton" <akpm@...ux-foundation.org>,
	linux-mm <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"Oleg Nesterov" <oleg@...sign.ru>,
	"David Howells" <dhowells@...hat.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"Christoph Hellwig" <chellwig@...ibm.com>,
	"Al Viro" <viro@...iv.linux.org.uk>,
	"Hugh Dickins" <hugh@...itas.com>, "Bryan Wu" <Bryan.Wu@...log.com>
Subject: Re: [PATCH] procfs task exe symlink

On Feb 19, 2008 4:54 PM, Matt Helsley <matthltc@...ibm.com> wrote:
> On Sat, 2008-02-16 at 07:12 -0500, Mike Frysinger wrote:
> > On Feb 6, 2008 8:44 PM, Matt Helsley <matthltc@...ibm.com> wrote:
> > > The kernel implements readlink of /proc/pid/exe by getting the file from the
> > > first executable VMA. Then the path to the file is reconstructed and reported as
> > > the result.
> > >
> > > Because of the VMA walk the code is slightly different on nommu systems. This
> > > patch avoids separate /proc/pid/exe code on nommu systems. Instead of walking
> > > the VMAs to find the first executable file-backed VMA we store a reference to
> > > the exec'd file in the mm_struct.
> > >
> > > That reference would prevent the filesystem holding the executable file from
> > > being unmounted even after unmapping the VMAs. So we track the number of
> > > VM_EXECUTABLE VMAs and drop the new reference when the last one is unmapped.
> > > This avoids pinning the mounted filesystem.
> > >
> > > Andrew, these are the updates I promised. Please consider this patch for
> > > inclusion in -mm.
> >
> > mm/nommu.c wasnt compiled tested, it's trivially broken:
>
> Thanks for the report. I've looked into this and the "obvious" fix,
> using vma->vm_mm, isn't correct since it's never set. This means the
> portions of the procfs task exe symlink patch using vma->vm_mm in
> mm/nommu.c are incorrect.
>
> The patch below attempts to fix this by using current->mm during mmap
> and passing the current mm to put_vma() as well.
>
> Mike, does this patch fix the compile problem(s)?

thanks, that does fix compiling.

> Mike, I don't have a nommu compile or test environment. I have yet
> to to generate a good CONFIG_MMU=n config on i386 (got one?). Since I
> don't have any nommu hardware I'm also looking into using qemu. It looks
> like I may need to build my own image from scratch. Do you have any
> recommendations on testing nommu configs without hardware?

it should be easy to cross-compile a kernel for the Blackfin
processor, but there is no qemu port.  the Blackfin port is the only
one ive done with no-mmu, so i cant comment on any other port.
-mike
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