Commit c6a80936 authored Jul 29, 2025 by Hannes Reinecke Committed by Andrew Morton Oct 03, 2025

drivers/base/memory: add node id parameter to add_memory_block()

Patch series "mm/memory_hotplug: fixup crash during uevent handling", v4.

we have some udev rules trying to read the sysfs attribute 'valid_zones'
during an memory 'add' event, causing a crash in zone_for_pfn_range(). 
Debugging found that mem->nid was set to NUMA_NO_NODE, which crashed in
NODE_DATA(nid).  Further analysis revealed that we're running into a race
with udev event processing: add_memory_resource() has this function calls:

1) __try_online_node()
2) arch_add_memory()
3) create_memory_block_devices()
  -> calls device_register() -> memory 'add' event
4) node_set_online()/__register_one_node()
  -> calls device_register() -> node 'add' event
5) register_memory_blocks_under_node()
  -> sets mem->nid

Which, to the uninitated, is ... weird ...

Why do we try to online the node in 1), but only register the node in 4)
_after_ we have created the memory blocks in 3) ?  And why do we set the
'nid' value in 5), when the uevent (which might need to see the correct
'nid' value) is sent out in 3) ?  There must be a reason, I'm sure ...

So here's a small patchset to fixup uevent ordering.  The first patch adds
a 'nid' parameter to add_memory_blocks() (to avoid mem->nid being
initialized with NUMA_NO_NODE), and the second patch reshuffles the code
in add_memory_resource() to fully initialize the node prior to calling
create_memory_block_devices() so that the node is valid at that time and
uevent processing will see correct values in sysfs.


This patch (of 3):

We have some udev rules trying to read the sysfs attribute 'valid_zones'
during an memory 'add' event, causing a crash in zone_for_pfn_range(). 
Debugging found that mem->nid was set to NUMA_NO_NODE, which crashed in
NODE_DATA(nid).  Further analysis revealed that we're running into a race
with udev event processing: add_memory_resource() has this function calls:

1) __try_online_node()
2) arch_add_memory()
3) create_memory_block_devices()
  -> calls device_register() -> memory 'add' event
4) node_set_online()/__register_one_node()
  -> calls device_register() -> node 'add' event
5) register_memory_blocks_under_node()
  -> sets mem->nid

Which, to the uninitated, is ... weird ...

Why do we try to online the node in 1), but only register the node in 4)
_after_ we have created the memory blocks in 3) ?  And why do we set the
'nid' value in 5), when the uevent (which might need to see the correct
'nid' value) is sent out in 3) ?  There must be a reason, I'm sure ...

So here's a small patchset to fixup uevent ordering.  The first patch adds
a 'nid' parameter to add_memory_blocks() (to avoid mem->nid being
initialized with NUMA_NO_NODE), and the second patch reshuffles the code
in add_memory_resource() to fully initialize the node prior to calling
create_memory_block_devices() so that the node is valid at that time and
uevent processing will see correct values in sysfs.


This patch (of 3):

Add a 'nid' parameter to add_memory_block() to initialize the memory block
with the correct node id.

Link: https://lkml.kernel.org/r/20250729064637.51662-1-hare@kernel.org
Link: https://lkml.kernel.org/r/20250729064637.51662-2-hare@kernel.org


Signed-off-by: Hannes Reinecke <hare@kernel.org>
Acked-by: David Hildenbrand <david@redhat.com>
Acked-by: Oscar Salvador <osalvador@suse.de>
Reviewed-by: Donet Tom <donettom@linux.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

parent 1367da7e

drivers/base/memory.c

+4 −11

Original line number	Diff line number	Diff line
		@@ -809,7 +809,7 @@ void memory_block_add_nid(struct memory_block *mem, int nid,
		}
		#endif

		static int add_memory_block(unsigned long block_id, unsigned long state,
		static int add_memory_block(unsigned long block_id, int nid, unsigned long state,
		struct vmem_altmap *altmap,
		struct memory_group *group)
		{
		@@ -827,7 +827,7 @@ static int add_memory_block(unsigned long block_id, unsigned long state,

		mem->start_section_nr = block_id * sections_per_block;
		mem->state = state;
		mem->nid = NUMA_NO_NODE;
		mem->nid = nid;
		mem->altmap = altmap;
		INIT_LIST_HEAD(&mem->group_next);

		@@ -854,13 +854,6 @@ static int add_memory_block(unsigned long block_id, unsigned long state,
		return 0;
		}

		static int add_hotplug_memory_block(unsigned long block_id,
		struct vmem_altmap *altmap,
		struct memory_group *group)
		{
		return add_memory_block(block_id, MEM_OFFLINE, altmap, group);
		}

		static void remove_memory_block(struct memory_block *memory)
		{
		if (WARN_ON_ONCE(memory->dev.bus != &memory_subsys))
		@@ -900,7 +893,7 @@ int create_memory_block_devices(unsigned long start, unsigned long size,
		return -EINVAL;

		for (block_id = start_block_id; block_id != end_block_id; block_id++) {
		ret = add_hotplug_memory_block(block_id, altmap, group);
		ret = add_memory_block(block_id, NUMA_NO_NODE, MEM_OFFLINE, altmap, group);
		if (ret)
		break;
		}
		@@ -1005,7 +998,7 @@ void __init memory_dev_init(void)
		continue;

		block_id = memory_block_id(nr);
		ret = add_memory_block(block_id, MEM_ONLINE, NULL, NULL);
		ret = add_memory_block(block_id, NUMA_NO_NODE, MEM_ONLINE, NULL, NULL);
		if (ret) {
		panic("%s() failed to add memory block: %d\n",
		__func__, ret);