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Date:   Wed, 24 Apr 2019 12:25:11 +0200
From:   David Hildenbrand <>
        Dan Williams <>,
        David Hildenbrand <>,
        Greg Kroah-Hartman <>,
        "Rafael J. Wysocki" <>,
        Alex Deucher <>,
        "David S. Miller" <>,
        Mark Brown <>,
        Chris Wilson <>,
        Oscar Salvador <>,
        Jonathan Cameron <>
Subject: [PATCH v1 7/7] mm/memory_hotplug: Make unregister_memory_block_under_nodes() never fail

We really don't want anything during memory hotunplug to fail.
We always pass a valid memory block device, that check can go. Avoid
allocating memory and eventually failing. As we are always called under
lock, we can use a static piece of memory. This avoids having to put
the structure onto the stack, having to guess about the stack size
of callers.

Patch inspired by a patch from Oscar Salvador.

In the future, there might be no need to iterate over nodes at all.
mem->nid should tell us exactly what to remove. Memory block devices
with mixed nodes (added during boot) should properly fenced off and never

Cc: Greg Kroah-Hartman <>
Cc: "Rafael J. Wysocki" <>
Cc: Alex Deucher <>
Cc: "David S. Miller" <>
Cc: Mark Brown <>
Cc: Chris Wilson <>
Cc: David Hildenbrand <>
Cc: Oscar Salvador <>
Cc: Andrew Morton <>
Cc: Jonathan Cameron <>
Signed-off-by: David Hildenbrand <>
 drivers/base/node.c  | 18 +++++-------------
 include/linux/node.h |  5 ++---
 2 files changed, 7 insertions(+), 16 deletions(-)

diff --git a/drivers/base/node.c b/drivers/base/node.c
index 04fdfa99b8bc..9be88fd05147 100644
--- a/drivers/base/node.c
+++ b/drivers/base/node.c
@@ -803,20 +803,14 @@ int register_mem_sect_under_node(struct memory_block *mem_blk, void *arg)
  * Unregister memory block device under all nodes that it spans.
+ * Has to be called with mem_sysfs_mutex held (due to unlinked_nodes).
-int unregister_memory_block_under_nodes(struct memory_block *mem_blk)
+void unregister_memory_block_under_nodes(struct memory_block *mem_blk)
-	NODEMASK_ALLOC(nodemask_t, unlinked_nodes, GFP_KERNEL);
 	unsigned long pfn, sect_start_pfn, sect_end_pfn;
+	static nodemask_t unlinked_nodes;
-	if (!mem_blk) {
-		NODEMASK_FREE(unlinked_nodes);
-		return -EFAULT;
-	}
-	if (!unlinked_nodes)
-		return -ENOMEM;
-	nodes_clear(*unlinked_nodes);
+	nodes_clear(unlinked_nodes);
 	sect_start_pfn = section_nr_to_pfn(mem_blk->start_section_nr);
 	sect_end_pfn = section_nr_to_pfn(mem_blk->end_section_nr);
 	for (pfn = sect_start_pfn; pfn <= sect_end_pfn; pfn++) {
@@ -827,15 +821,13 @@ int unregister_memory_block_under_nodes(struct memory_block *mem_blk)
 		if (!node_online(nid))
-		if (node_test_and_set(nid, *unlinked_nodes))
+		if (node_test_and_set(nid, unlinked_nodes))
-	NODEMASK_FREE(unlinked_nodes);
-	return 0;
 int link_mem_sections(int nid, unsigned long start_pfn, unsigned long end_pfn)
diff --git a/include/linux/node.h b/include/linux/node.h
index 02a29e71b175..548c226966a2 100644
--- a/include/linux/node.h
+++ b/include/linux/node.h
@@ -139,7 +139,7 @@ extern int register_cpu_under_node(unsigned int cpu, unsigned int nid);
 extern int unregister_cpu_under_node(unsigned int cpu, unsigned int nid);
 extern int register_mem_sect_under_node(struct memory_block *mem_blk,
 						void *arg);
-extern int unregister_memory_block_under_nodes(struct memory_block *mem_blk);
+extern void unregister_memory_block_under_nodes(struct memory_block *mem_blk);
 extern int register_memory_node_under_compute_node(unsigned int mem_nid,
 						   unsigned int cpu_nid,
@@ -175,9 +175,8 @@ static inline int register_mem_sect_under_node(struct memory_block *mem_blk,
 	return 0;
-static inline int unregister_memory_block_under_nodes(struct memory_block *mem_blk)
+static inline void unregister_memory_block_under_nodes(struct memory_block *mem_blk)
-	return 0;
 static inline void register_hugetlbfs_with_node(node_registration_func_t reg,

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