acpi/hmat: Fix lockdep warning for hmem_register_resource()

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: cf8741ac57ed ("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>

diff --git a/drivers/acpi/numa/hmat.c b/drivers/acpi/numa/hmat.c
index 5a36d57289b43d3c20a2ed23abadb759ffa96f0b..11e4483685c9cff9f1497842cdfea0b7e60b3d2c 100644 (file)
--- a/drivers/acpi/numa/hmat.c
+++ b/drivers/acpi/numa/hmat.c
@@ -874,10 +874,32 @@ static void hmat_register_target_devices(struct memory_target *target)
        }
 }
 
-static void hmat_register_target(struct memory_target *target)
+static void hmat_hotplug_target(struct memory_target *target)
 {
        int nid = pxm_to_node(target->memory_pxm);
 
+       /*
+        * Skip offline nodes. This can happen when memory marked EFI_MEMORY_SP,
+        * "specific purpose", is applied to all the memory in a proximity
+        * domain leading to * the node being marked offline / unplugged, or if
+        * memory-only "hotplug" node is offline.
+        */
+       if (nid == NUMA_NO_NODE || !node_online(nid))
+               return;
+
+       guard(mutex)(&target_lock);
+       if (target->registered)
+               return;
+
+       hmat_register_target_initiators(target);
+       hmat_register_target_cache(target);
+       hmat_register_target_perf(target, ACCESS_COORDINATE_LOCAL);
+       hmat_register_target_perf(target, ACCESS_COORDINATE_CPU);
+       target->registered = true;
+}
+
+static void hmat_register_target(struct memory_target *target)
+{
        /*
         * Devices may belong to either an offline or online
         * node, so unconditionally add them.
@@ -895,25 +917,7 @@ static void hmat_register_target(struct memory_target *target)
        }
        mutex_unlock(&target_lock);
 
-       /*
-        * Skip offline nodes. This can happen when memory
-        * marked EFI_MEMORY_SP, "specific purpose", is applied
-        * to all the memory in a proximity domain leading to
-        * the node being marked offline / unplugged, or if
-        * memory-only "hotplug" node is offline.
-        */
-       if (nid == NUMA_NO_NODE || !node_online(nid))
-               return;
-
-       mutex_lock(&target_lock);
-       if (!target->registered) {
-               hmat_register_target_initiators(target);
-               hmat_register_target_cache(target);
-               hmat_register_target_perf(target, ACCESS_COORDINATE_LOCAL);
-               hmat_register_target_perf(target, ACCESS_COORDINATE_CPU);
-               target->registered = true;
-       }
-       mutex_unlock(&target_lock);
+       hmat_hotplug_target(target);
 }
 
 static void hmat_register_targets(void)
@@ -939,7 +943,7 @@ static int hmat_callback(struct notifier_block *self,
        if (!target)
                return NOTIFY_OK;
 
-       hmat_register_target(target);
+       hmat_hotplug_target(target);
        return NOTIFY_OK;
 }