[PATCH 0/2] mm/memory_hotplug: fixup crash during uevent handling

[Hannes Reinecke <hare@kernel.org>]

From: Hannes Reinecke <hare@suse.de>

Hi all,

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.

As usual, comments and reviews are welcome.

Hannes Reinecke (2):
  drivers/base/memory: add node id parameter to add_memory_block()
  mm/memory_hotplug: activate node before adding new memory blocks

 drivers/base/memory.c  | 32 ++++++++++++--------------------
 include/linux/memory.h |  2 +-
 mm/memory_hotplug.c    | 32 +++++++++++++++++---------------
 3 files changed, 30 insertions(+), 36 deletions(-)

-- 
2.43.0