linux-kernel - [bug ?] do_get

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Date:	Thu, 3 Jul 2008 16:44:58 -0400
From:	John Blackwood <john.blackwood@...r.com>
To:	<linux-kernel@...r.kernel.org>
CC:	Lee Schermerhorn <lee.schermerhorn@...com>,
	Joe Korty <joe.korty@...r.com>
Subject: [bug ?] do_get_mempolicy()

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make this line of code no longer valid ?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.

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