cxl/region: Fix a race condition in memory hotplug notifier

In the memory hotplug notifier function of the CXL region,
cxl_region_perf_attrs_callback(), the node ID is obtained by checking
the host address range of the region. However, the address range
information is not available when the region is registered in
devm_cxl_add_region(). Additionally, this information may be removed
or added under the protection of cxl_region_rwsem during runtime. If
the memory notifier is called for nodes other than that backed by the
region, a race condition may occur, potentially leading to a NULL
dereference or an invalid address range.

The race condition is addressed by checking the availability of the
address range information under the protection of cxl_region_rwsem. To
enhance code readability and use guard(), the relevant code has been
moved into a newly added function: cxl_region_nid().

Fixes: 067353a46d8c ("cxl/region: Add memory hotplug notifier for cxl region")
Signed-off-by: Huang, Ying <[email protected]>
Cc: Dan Williams <[email protected]>
Cc: Alison Schofield <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Jonathan Cameron <[email protected]>
Cc: Dave Jiang <[email protected]>
Cc: Bharata B Rao <[email protected]>
Cc: Alistair Popple <[email protected]>
Cc: Aneesh Kumar K.V <[email protected]>
Cc: Davidlohr Bueso <[email protected]>
Cc: Vishal Verma <[email protected]>
Cc: Ira Weiny <[email protected]>
Reviewed-by: Jonathan Cameron <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Dave Jiang <[email protected]>

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