[PATCH v3 0/2] acpi/hmat: hmat_register_target() refactor to address lockdep warning

[PATCH v3 0/2] acpi/hmat: hmat_register_target() refactor to address lockdep warning

[Dave Jiang]

This series has changes that refactor the hmat_register_target() function
to clean up a lockdep warning.

Dave Jiang (2):
  acpi/hmat: Return when generic target is updated
  acpi/hmat: Fix lockdep warning for hmem_register_resource()

 drivers/acpi/numa/hmat.c | 47 ++++++++++++++++++++++------------------
 1 file changed, 26 insertions(+), 21 deletions(-)


base-commit: 3a8660878839faadb4f1a6dd72c3179c1df56787
-- 
2.51.0

[PATCH v3 1/2] acpi/hmat: Return when generic target is updated

[Dave Jiang]

With the current code flow, once the generic target is updated
target->registered is set and the remaining code is skipped.
So return immediately instead of going through the checks and
then skip.

Signed-off-by: Dave Jiang <dave.jiang@intel.com>
---
 drivers/acpi/numa/hmat.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/drivers/acpi/numa/hmat.c b/drivers/acpi/numa/hmat.c
index 5a36d57289b4..1dc73d20d989 100644
--- a/drivers/acpi/numa/hmat.c
+++ b/drivers/acpi/numa/hmat.c
@@ -888,12 +888,13 @@ static void hmat_register_target(struct memory_target *target)
 	 * Register generic port perf numbers. The nid may not be
 	 * initialized and is still NUMA_NO_NODE.
 	 */
-	mutex_lock(&target_lock);
-	if (*(u16 *)target->gen_port_device_handle) {
-		hmat_update_generic_target(target);
-		target->registered = true;
+	scoped_guard(mutex, &target_lock) {
+		if (*(u16 *)target->gen_port_device_handle) {
+			hmat_update_generic_target(target);
+			target->registered = true;
+			return;
+		}
 	}
-	mutex_unlock(&target_lock);
 
 	/*
 	 * Skip offline nodes. This can happen when memory
-- 
2.51.0

[PATCH v3 2/2] acpi/hmat: Fix lockdep warning for hmem_register_resource()

[Dave Jiang]

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.

Fixes: cf8741ac57ed ("ACPI: NUMA: HMAT: Register "soft reserved" memory as a
n "hmem" device")
notmuch/
Signed-off-by: Dave Jiang <dave.jiang@intel.com>

---
v3:
- Refactor to split out target device setup vs target update (Dan)
---
 drivers/acpi/numa/hmat.c | 48 ++++++++++++++++++++++------------------
 1 file changed, 26 insertions(+), 22 deletions(-)

diff --git a/drivers/acpi/numa/hmat.c b/drivers/acpi/numa/hmat.c
index 1dc73d20d989..ddbdd32e79a8 100644
--- a/drivers/acpi/numa/hmat.c
+++ b/drivers/acpi/numa/hmat.c
@@ -874,28 +874,10 @@ 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);
 
-	/*
-	 * Devices may belong to either an offline or online
-	 * node, so unconditionally add them.
-	 */
-	hmat_register_target_devices(target);
-
-	/*
-	 * Register generic port perf numbers. The nid may not be
-	 * initialized and is still NUMA_NO_NODE.
-	 */
-	scoped_guard(mutex, &target_lock) {
-		if (*(u16 *)target->gen_port_device_handle) {
-			hmat_update_generic_target(target);
-			target->registered = true;
-			return;
-		}
-	}
-
 	/*
 	 * Skip offline nodes. This can happen when memory
 	 * marked EFI_MEMORY_SP, "specific purpose", is applied
@@ -906,7 +888,7 @@ static void hmat_register_target(struct memory_target *target)
 	if (nid == NUMA_NO_NODE || !node_online(nid))
 		return;
 
-	mutex_lock(&target_lock);
+	guard(mutex)(&target_lock);
 	if (!target->registered) {
 		hmat_register_target_initiators(target);
 		hmat_register_target_cache(target);
@@ -914,7 +896,29 @@ static void hmat_register_target(struct memory_target *target)
 		hmat_register_target_perf(target, ACCESS_COORDINATE_CPU);
 		target->registered = true;
 	}
-	mutex_unlock(&target_lock);
+}
+
+static void hmat_register_target(struct memory_target *target)
+{
+	/*
+	 * Devices may belong to either an offline or online
+	 * node, so unconditionally add them.
+	 */
+	hmat_register_target_devices(target);
+
+	/*
+	 * Register generic port perf numbers. The nid may not be
+	 * initialized and is still NUMA_NO_NODE.
+	 */
+	scoped_guard(mutex, &target_lock) {
+		if (*(u16 *)target->gen_port_device_handle) {
+			hmat_update_generic_target(target);
+			target->registered = true;
+			return;
+		}
+	}
+
+	hmat_hotplug_target(target);
 }
 
 static void hmat_register_targets(void)
@@ -940,7 +944,7 @@ static int hmat_callback(struct notifier_block *self,
 	if (!target)
 		return NOTIFY_OK;
 
-	hmat_register_target(target);
+	hmat_hotplug_target(target);
 	return NOTIFY_OK;
 }
 
-- 
2.51.0

Re: [PATCH v3 1/2] acpi/hmat: Return when generic target is updated

[Jonathan Cameron]

On Fri, 17 Oct 2025 14:21:04 -0700
Dave Jiang <dave.jiang@intel.com> wrote:

> With the current code flow, once the generic target is updated
> target->registered is set and the remaining code is skipped.
> So return immediately instead of going through the checks and
> then skip.
> 
> Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>

Re: [PATCH v3 2/2] acpi/hmat: Fix lockdep warning for hmem_register_resource()

[Jonathan Cameron]

On Fri, 17 Oct 2025 14:21:05 -0700
Dave Jiang <dave.jiang@intel.com> wrote:

> 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.
> 
> Fixes: cf8741ac57ed ("ACPI: NUMA: HMAT: Register "soft reserved" memory as a
> n "hmem" device")
Fix up whatever caused that line to wrap!

> notmuch/

?

> Signed-off-by: Dave Jiang <dave.jiang@intel.com>

The guard change seems to be unrelated to rest of the patch.
Probably shouldn't be here.

> 
> ---
> v3:
> - Refactor to split out target device setup vs target update (Dan)
> ---
>  drivers/acpi/numa/hmat.c | 48 ++++++++++++++++++++++------------------
>  1 file changed, 26 insertions(+), 22 deletions(-)
> 
> diff --git a/drivers/acpi/numa/hmat.c b/drivers/acpi/numa/hmat.c
> index 1dc73d20d989..ddbdd32e79a8 100644
> --- a/drivers/acpi/numa/hmat.c
> +++ b/drivers/acpi/numa/hmat.c
> @@ -874,28 +874,10 @@ 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)
>  {

> @@ -906,7 +888,7 @@ static void hmat_register_target(struct memory_target *target)
>  	if (nid == NUMA_NO_NODE || !node_online(nid))
>  		return;
>  
> -	mutex_lock(&target_lock);
> +	guard(mutex)(&target_lock);
Smells unrelated...

If you did want to do this I'd also do
	if (target->registered)
		return;

	hmat_register_target_initiators();
etc.


>  	if (!target->registered) {
>  		hmat_register_target_initiators(target);
>  		hmat_register_target_cache(target);
> @@ -914,7 +896,29 @@ static void hmat_register_target(struct memory_target *target)
>  		hmat_register_target_perf(target, ACCESS_COORDINATE_CPU);
>  		target->registered = true;
>  	}
> -	mutex_unlock(&target_lock);
> +}

[PATCH v3 2/2] acpi/hmat: Fix lockdep warning for hmem_register_resource()

[Dave Jiang]

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.

Fixes: cf8741ac57ed ("ACPI: NUMA: HMAT: Register "soft reserved" memory as a
n "hmem" device")
notmuch/
Signed-off-by: Dave Jiang <dave.jiang@intel.com>

---
v3:
- Refactor to split out target device setup vs target update (Dan)
---
 drivers/acpi/numa/hmat.c | 48 ++++++++++++++++++++++------------------
 1 file changed, 26 insertions(+), 22 deletions(-)

diff --git a/drivers/acpi/numa/hmat.c b/drivers/acpi/numa/hmat.c
index 1dc73d20d989..ddbdd32e79a8 100644
--- a/drivers/acpi/numa/hmat.c
+++ b/drivers/acpi/numa/hmat.c
@@ -874,28 +874,10 @@ 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);
 
-	/*
-	 * Devices may belong to either an offline or online
-	 * node, so unconditionally add them.
-	 */
-	hmat_register_target_devices(target);
-
-	/*
-	 * Register generic port perf numbers. The nid may not be
-	 * initialized and is still NUMA_NO_NODE.
-	 */
-	scoped_guard(mutex, &target_lock) {
-		if (*(u16 *)target->gen_port_device_handle) {
-			hmat_update_generic_target(target);
-			target->registered = true;
-			return;
-		}
-	}
-
 	/*
 	 * Skip offline nodes. This can happen when memory
 	 * marked EFI_MEMORY_SP, "specific purpose", is applied
@@ -906,7 +888,7 @@ static void hmat_register_target(struct memory_target *target)
 	if (nid == NUMA_NO_NODE || !node_online(nid))
 		return;
 
-	mutex_lock(&target_lock);
+	guard(mutex)(&target_lock);
 	if (!target->registered) {
 		hmat_register_target_initiators(target);
 		hmat_register_target_cache(target);
@@ -914,7 +896,29 @@ static void hmat_register_target(struct memory_target *target)
 		hmat_register_target_perf(target, ACCESS_COORDINATE_CPU);
 		target->registered = true;
 	}
-	mutex_unlock(&target_lock);
+}
+
+static void hmat_register_target(struct memory_target *target)
+{
+	/*
+	 * Devices may belong to either an offline or online
+	 * node, so unconditionally add them.
+	 */
+	hmat_register_target_devices(target);
+
+	/*
+	 * Register generic port perf numbers. The nid may not be
+	 * initialized and is still NUMA_NO_NODE.
+	 */
+	scoped_guard(mutex, &target_lock) {
+		if (*(u16 *)target->gen_port_device_handle) {
+			hmat_update_generic_target(target);
+			target->registered = true;
+			return;
+		}
+	}
+
+	hmat_hotplug_target(target);
 }
 
 static void hmat_register_targets(void)
@@ -940,7 +944,7 @@ static int hmat_callback(struct notifier_block *self,
 	if (!target)
 		return NOTIFY_OK;
 
-	hmat_register_target(target);
+	hmat_hotplug_target(target);
 	return NOTIFY_OK;
 }
 
-- 
2.51.0