From: zhong jiang zhongjiang@huawei.com Subject: mm/mempolicy.c: fix an incorrect rebind node in mpol_rebind_nodemask

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@suse.cz: new changlog] Link: http://lkml.kernel.org/r/ef6a69c6-c052-b067-8f2c-9d615c619bb9@suse.cz Link: http://lkml.kernel.org/r/1558768043-23184-1-git-send-email-zhongjiang@huawei... Fixes: 213980c0f23b ("mm, mempolicy: simplify rebinding mempolicies when updating cpusets") Signed-off-by: zhong jiang zhongjiang@huawei.com Reviewed-by: Vlastimil Babka vbabka@suse.cz Cc: Oscar Salvador osalvador@suse.de Cc: Anshuman Khandual khandual@linux.vnet.ibm.com Cc: Michal Hocko mhocko@suse.com Cc: Mel Gorman mgorman@techsingularity.net Cc: Andrea Arcangeli aarcange@redhat.com Cc: Ralph Campbell rcampbell@nvidia.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

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

--- a/mm/mempolicy.c~mm-mempolicy-fix-an-incorrect-rebind-node-in-mpol_rebind_nodemask +++ a/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)) _