linux-kernel - [PATCH] mm/mempolicy.c: forbid static or relative flags for local NUMA mode

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Date:   Sun, 18 Sep 2016 13:29:43 +0200
From:   Piotr Kwapulinski <kwapulinski.piotr@...il.com>
To:     akpm@...ux-foundation.org
Cc:     kirill.shutemov@...ux.intel.com, vbabka@...e.cz,
        rientjes@...gle.com, mhocko@...nel.org,
        mgorman@...hsingularity.net, liangchen.linux@...il.com,
        nzimmer@....com, linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        kwapulinski.piotr@...il.com
Subject: [PATCH] mm/mempolicy.c: forbid static or relative flags for local NUMA mode

The MPOL_F_STATIC_NODES and MPOL_F_RELATIVE_NODES flags are irrelevant
when setting them for MPOL_LOCAL NUMA memory policy via set_mempolicy.
Return the "invalid argument" from set_mempolicy whenever
any of these flags is passed along with MPOL_LOCAL.
It is consistent with MPOL_PREFERRED passed with empty nodemask.
It also slightly shortens the execution time in paths where these flags
are used e.g. when trying to rebind the NUMA nodes for changes in
cgroups cpuset mems (mpol_rebind_preferred()) or when just printing
the mempolicy structure (/proc/PID/numa_maps).
Isolated tests done.

Signed-off-by: Piotr Kwapulinski <kwapulinski.piotr@...il.com>
---
 mm/mempolicy.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 2da72a5..27b07d1 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -276,7 +276,9 @@ static struct mempolicy *mpol_new(unsigned short mode, unsigned short flags,
 				return ERR_PTR(-EINVAL);
 		}
 	} else if (mode == MPOL_LOCAL) {
-		if (!nodes_empty(*nodes))
+		if (!nodes_empty(*nodes) ||
+		    (flags & MPOL_F_STATIC_NODES) ||
+		    (flags & MPOL_F_RELATIVE_NODES))
 			return ERR_PTR(-EINVAL);
 		mode = MPOL_PREFERRED;
 	} else if (nodes_empty(*nodes))
-- 
2.9.2