Message-ID: <486D3A4A.6000502@ccur.com>
Date: Thu, 3 Jul 2008 16:44:58 -0400
From: John Blackwood <john.blackwood@ccur.com>
User-Agent: Thunderbird 2.0.0.14 (X11/20080421)
MIME-Version: 1.0
To: <linux-kernel@vger.kernel.org>
CC: Lee Schermerhorn <lee.schermerhorn@hp.com>, Joe Korty <joe.korty@ccur.com>
Subject: [bug ?] do_get_mempolicy()
Content-Type: text/plain; charset="ISO-8859-1"; format=flowed
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1301
Lines: 36

Hi Lee,

I'm having unexpected results with get_mempolicy(2) in 2.6.26, and
I am hoping that you can either agree with me, or maybe comment on my
misconceptions.

When I have a task with no special task mempolicy (the default mempolicy),
when I call get_mempolicy(2), it returns a policy value of 2 (MPOL_BIND)
with a NULL nodemask.

I believe that this is because of the code in do_get_mempolicy() that does:

  *policy |= pol->flags;

in the else case when flags do not contain MPOL_F_NODE.

I guess I don't understand why we are ORing in the pol->flags into the
*policy value.  For example, when this is for the default_policy, the
MPOL_F_LOCAL flag (which has a value of 2) gets stuffed into the *policy
location, and a get_mempolicy(2) caller sees this as the MPOL_BIND
mempolicy.

Maybe the "*policy |= pol->flags;" line should be removed ?

That is, maybe it was valid at some point, but subsequent changes
make this line of code no longer valid ?

Sorry if I'm out-to-lunch here...

Thanks very much for you time and considerations on this issue.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/