[PATCH v3 10/11] mm/memory_hotplug: Make unregister_memory_block_under_nodes() never fail

From: David Hildenbrand
Date: Mon May 27 2019 - 07:16:21 EST

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 <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: "Rafael J. Wysocki" <rafael@xxxxxxxxxx>
Cc: Alex Deucher <alexander.deucher@xxxxxxx>
Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
Cc: Mark Brown <broonie@xxxxxxxxxx>
Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Oscar Salvador <osalvador@xxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
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,