linux-kernel - Re: [RFC v10][PATCH 05/13] Dump memory address space

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Date:	Mon, 01 Dec 2008 10:00:12 -0800
From:	Dave Hansen <dave@...ux.vnet.ibm.com>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	Oren Laadan <orenl@...columbia.edu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...l.org>,
	containers@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linux-api@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Serge Hallyn <serue@...ibm.com>, Ingo Molnar <mingo@...e.hu>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [RFC v10][PATCH 05/13] Dump memory address space

On Fri, 2008-11-28 at 10:53 +0000, Al Viro wrote:
> 
> > +static int cr_ctx_checkpoint(struct cr_ctx *ctx, pid_t pid)
> > +{
> > +     ctx->root_pid = pid;
> > +
> > +     /*
> > +      * assume checkpointer is in container's root vfs
> > +      * FIXME: this works for now, but will change with real containers
> > +      */
> > +     ctx->vfsroot = &current->fs->root;
> > +     path_get(ctx->vfsroot);
> 
> This is going to break as soon as you get another thread doing e.g. chroot(2)
> while you are in there.

Yeah, we do need at least a read_lock(&current->fs->lock) to keep people
from chroot()'ing underneath us.

> And it's a really, _really_ bad idea to take a
> pointer to shared object, increment refcount on the current *contents* of
> said object and assume that dropping refcount on the later contents of the
> same will balance out.

Absolutely.  I assume you mean get_fs_struct(current) instead of
path_get().

-- Dave

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