+ mm-mempolicy-ignore-a-bind-policy-whose-nodes-have-no-memory.patch added to mm-new branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm/mempolicy: ignore a bind policy whose nodes have no memory
has been added to the -mm mm-new branch.  Its filename is
     mm-mempolicy-ignore-a-bind-policy-whose-nodes-have-no-memory.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-mempolicy-ignore-a-bind-policy-whose-nodes-have-no-memory.patch

This patch will later appear in the mm-new branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Note, mm-new is a provisional staging ground for work-in-progress
patches, and acceptance into mm-new is a notification for others take
notice and to finish up reviews.  Please do not hesitate to respond to
review feedback and post updated versions to replace or incrementally
fixup patches in mm-new.

The mm-new branch of mm.git is not included in linux-next

If a few days of testing in mm-new is successful, the patch will me moved
into mm.git's mm-unstable branch, which is included in linux-next

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------------------------------------------------------
From: "Gregory Price (Meta)" <gourry@gourry.net>
Subject: mm/mempolicy: ignore a bind policy whose nodes have no memory
Date: Fri, 13 Nov 2026 14:26:42 -0500

apply_policy_zone() assumes that policy->nodes intersects N_MEMORY, so
it reads a bind policy with no N_HIGH_MEMORY node as movable-only.

On systems with CONFIG_CPUSETS=n, nothing rebinds policies when memory
is removed, so offlining all memory on the nodes a bind policy names
leaves it with none. The policy is then treated as movable-only, and
movable allocations are restricted to nodes without memory.

This results in allocations failures, a VM_FAULT_OOM leak, and then
an infinitely retrying fault that hangs the process.

  page allocation failure: order:0, mode:0x140dca ... nodemask=2
  Huh VM_FAULT_OOM leaked out to the #PF handler. Retrying PF

Ignore a bind policy whose nodes have no memory. policy_nodemask()
already ignores a bind policy that does not intersect the cpuset.
This covers hugetlb's policy_mbind_nodemask() as well.

If the nodes regain memory, the policy applies again.

CPUSETS=n with HOTREMOVE=y is unlikely a common configuration, so this
isn't marked for stable.

Link: https://lore.kernel.org/20261113192642.2618878-1-gourry@gourry.net
Signed-off-by: Gregory Price (Meta) <gourry@gourry.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Joshua Hahn <joshua.hahnjy@gmail.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: SJ Park <sj@kernel.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Rakie Kim <rakie.kim@sk.com>
Cc: Ying Huang <ying.huang@linux.alibaba.com>
---

 mm/mempolicy.c |    4 ++++
 1 file changed, 4 insertions(+)

--- a/mm/mempolicy.c~mm-mempolicy-ignore-a-bind-policy-whose-nodes-have-no-memory
+++ a/mm/mempolicy.c
@@ -2100,6 +2100,10 @@ bool apply_policy_zone(struct mempolicy
 
 	BUG_ON(dynamic_policy_zone == ZONE_MOVABLE);
 
+	/* Memory hot-remove can leave policy->nodes without memory. */
+	if (!nodes_intersects(policy->nodes, node_states[N_MEMORY]))
+		return false;
+
 	/*
 	 * if policy->nodes has movable memory only,
 	 * we apply policy when gfp_zone(gfp) = ZONE_MOVABLE only.
_

Patches currently in -mm which might be from gourry@gourry.net are

mm-memory-tiers-reset-demotion-targets-of-nodes-without-memory.patch
mm-mempolicy-convert-mempolicy-refcnt-to-refcount_t.patch
selftests-mm-add-madv_cold-and-madv_pageout-contract-tests.patch
selftests-mm-check-madv_cold-and-madv_pageout-range-handling.patch
selftests-mm-check-that-madv_cold-and-madv_pageout-reject-hugetlb.patch
selftests-mm-check-that-madv_cold-and-madv_pageout-preserve-shared-memory.patch
selftests-mm-check-madv_cold-and-madv_pageout-on-partly-advised-thps.patch
selftests-mm-check-madv_pageout-file-permissions.patch
selftests-mm-check-that-unauthorized-madv_pageout-skips-large-file-folios.patch
mm-mempolicy-ignore-a-bind-policy-whose-nodes-have-no-memory.patch
mm-hmm-reject-shadow-stack-mappings.patch