[PATCH 4.19 33/72] mm/mempolicy.c: fix an incorrect rebind node in mpol_rebind_nodemask

[Greg Kroah-Hartman]

From: zhong jiang <zhongjiang@xxxxxxxxxx>

commit 29b190fa774dd1b72a1a6f19687d55dc72ea83be upstream.

mpol_rebind_nodemask() is called for MPOL_BIND and MPOL_INTERLEAVE
mempoclicies when the tasks's cpuset's mems_allowed changes.  For
policies created without MPOL_F_STATIC_NODES or MPOL_F_RELATIVE_NODES,
it works by remapping the policy's allowed nodes (stored in v.nodes)
using the previous value of mems_allowed (stored in
w.cpuset_mems_allowed) as the domain of map and the new mems_allowed
(passed as nodes) as the range of the map (see the comment of
bitmap_remap() for details).

The result of remapping is stored back as policy's nodemask in v.nodes,
and the new value of mems_allowed should be stored in
w.cpuset_mems_allowed to facilitate the next rebind, if it happens.

However, 213980c0f23b ("mm, mempolicy: simplify rebinding mempolicies
when updating cpusets") introduced a bug where the result of remapping
is stored in w.cpuset_mems_allowed instead.  Thus, a mempolicy's
allowed nodes can evolve in an unexpected way after a series of
rebinding due to cpuset mems_allowed changes, possibly binding to a
wrong node or a smaller number of nodes which may e.g.  overload them.
This patch fixes the bug so rebinding again works as intended.

[vbabka@xxxxxxx: new changlog]
  Link: http://lkml.kernel.org/r/ef6a69c6-c052-b067-8f2c-9d615c619bb9@xxxxxxx
Link: http://lkml.kernel.org/r/1558768043-23184-1-git-send-email-zhongjiang@xxxxxxxxxx
Fixes: 213980c0f23b ("mm, mempolicy: simplify rebinding mempolicies when updating cpusets")
Signed-off-by: zhong jiang <zhongjiang@xxxxxxxxxx>
Reviewed-by: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Oscar Salvador <osalvador@xxxxxxx>
Cc: Anshuman Khandual <khandual@xxxxxxxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Ralph Campbell <rcampbell@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 mm/mempolicy.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -306,7 +306,7 @@ static void mpol_rebind_nodemask(struct
 	else {
 		nodes_remap(tmp, pol->v.nodes,pol->w.cpuset_mems_allowed,
 								*nodes);
-		pol->w.cpuset_mems_allowed = tmp;
+		pol->w.cpuset_mems_allowed = *nodes;
 	}
 
 	if (nodes_empty(tmp))