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[ Upstream commit214291cbaa] The following lockdep splat was observed while kernel auto-online a CXL memory region: ====================================================== WARNING: possible circular locking dependency detected 6.17.0djtest+ #53 Tainted: G W ------------------------------------------------------ systemd-udevd/3334 is trying to acquire lock: ffffffff90346188 (hmem_resource_lock){+.+.}-{4:4}, at: hmem_register_resource+0x31/0x50 but task is already holding lock: ffffffff90338890 ((node_chain).rwsem){++++}-{4:4}, at: blocking_notifier_call_chain+0x2e/0x70 which lock already depends on the new lock. [..] Chain exists of: hmem_resource_lock --> mem_hotplug_lock --> (node_chain).rwsem Possible unsafe locking scenario: CPU0 CPU1 ---- ---- rlock((node_chain).rwsem); lock(mem_hotplug_lock); lock((node_chain).rwsem); lock(hmem_resource_lock); The lock ordering can cause potential deadlock. There are instances where hmem_resource_lock is taken after (node_chain).rwsem, and vice versa. Split out the target update section of hmat_register_target() so that hmat_callback() only envokes that section instead of attempt to register hmem devices that it does not need to. [ dj: Fix up comment to be closer to 80cols. (Jonathan) ] Fixes:cf8741ac57("ACPI: NUMA: HMAT: Register "soft reserved" memory as an "hmem" device") Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com> Tested-by: Smita Koralahalli <Smita.KoralahalliChannabasappa@amd.com> Reviewed-by: Smita Koralahalli <Smita.KoralahalliChannabasappa@amd.com> Reviewed-by: Dan Williams <dan.j.williams@intel.com> Link: https://patch.msgid.link/20251105235115.85062-3-dave.jiang@intel.com Signed-off-by: Dave Jiang <dave.jiang@intel.com> Signed-off-by: Sasha Levin <sashal@kernel.org>