[PATCH v3 0/2] cxl: Fix nvdimm_bus race for nvdimm devices

[PATCH v3 0/2] cxl: Fix nvdimm_bus race for nvdimm devices

[Dave Jiang]

v3:
- Just move the symbol of devm_cxl_add_nvdimm_bridge() with a wrapper function. (Dan)
- Squash the functionality of patch 2 and 3. (Dan)
- Introduce a flag to invalidate cxl_nvdimm when releasing nvdimm_bus. (Dan)
- With cxl_nvdimm marked as "invalidated" no need the check in cxl_nvdimm_driver. (Dan)

v2:
- Try a different approach

A small series to address a race for nvdimm_bus object when using the
nvdimm_bridge object.

Dave Jiang (2):
  cxl: Move devm_cxl_add_nvdimm_bridge() to cxl_pmem.ko
  cxl: Fix race of nvdimm_bus object when creating nvdimm objects

 drivers/cxl/core/pmem.c | 40 ++++++++++++++++++++++++++++++----------
 drivers/cxl/cxl.h       |  7 +++++++
 drivers/cxl/pmem.c      | 22 +++++++++++++++++++++-
 3 files changed, 58 insertions(+), 11 deletions(-)


base-commit: 63fbf275fa9f18f7020fb8acf54fa107e51d0f23
-- 
2.53.0

[PATCH v3 1/2] cxl: Move devm_cxl_add_nvdimm_bridge() to cxl_pmem.ko

[Dave Jiang]

Moving the symbol devm_cxl_add_nvdimm_bridge() to
drivers/cxl/cxl_pmem.c, so that cxl_pmem can export a symbol that gives
cxl_acpi a depedency on cxl_pmem kernel module. This is a prepatory patch
to resolve the issue of a race for nvdimm_bus object that is created
during cxl_acpi_probe().

No functional changes besides moving code.

Suggested-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Dave Jiang <dave.jiang@intel.com>
---
v3:
- Just move the symbol with a wrapper function. (Dan)
---
 drivers/cxl/core/pmem.c | 13 +++----------
 drivers/cxl/cxl.h       |  2 ++
 drivers/cxl/pmem.c      | 14 ++++++++++++++
 3 files changed, 19 insertions(+), 10 deletions(-)

diff --git a/drivers/cxl/core/pmem.c b/drivers/cxl/core/pmem.c
index e7b1e6fa0ea0..7c78344acc6d 100644
--- a/drivers/cxl/core/pmem.c
+++ b/drivers/cxl/core/pmem.c
@@ -115,15 +115,8 @@ static void unregister_nvb(void *_cxl_nvb)
 	device_unregister(&cxl_nvb->dev);
 }
 
-/**
- * devm_cxl_add_nvdimm_bridge() - add the root of a LIBNVDIMM topology
- * @host: platform firmware root device
- * @port: CXL port at the root of a CXL topology
- *
- * Return: bridge device that can host cxl_nvdimm objects
- */
-struct cxl_nvdimm_bridge *devm_cxl_add_nvdimm_bridge(struct device *host,
-						     struct cxl_port *port)
+struct cxl_nvdimm_bridge *__devm_cxl_add_nvdimm_bridge(struct device *host,
+						       struct cxl_port *port)
 {
 	struct cxl_nvdimm_bridge *cxl_nvb;
 	struct device *dev;
@@ -155,7 +148,7 @@ struct cxl_nvdimm_bridge *devm_cxl_add_nvdimm_bridge(struct device *host,
 	put_device(dev);
 	return ERR_PTR(rc);
 }
-EXPORT_SYMBOL_NS_GPL(devm_cxl_add_nvdimm_bridge, "CXL");
+EXPORT_SYMBOL_FOR_MODULES(__devm_cxl_add_nvdimm_bridge, "cxl_pmem");
 
 static void cxl_nvdimm_release(struct device *dev)
 {
diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
index 04c673e7cdb0..f5850800f400 100644
--- a/drivers/cxl/cxl.h
+++ b/drivers/cxl/cxl.h
@@ -920,6 +920,8 @@ void cxl_driver_unregister(struct cxl_driver *cxl_drv);
 struct cxl_nvdimm_bridge *to_cxl_nvdimm_bridge(struct device *dev);
 struct cxl_nvdimm_bridge *devm_cxl_add_nvdimm_bridge(struct device *host,
 						     struct cxl_port *port);
+struct cxl_nvdimm_bridge *__devm_cxl_add_nvdimm_bridge(struct device *host,
+						       struct cxl_port *port);
 struct cxl_nvdimm *to_cxl_nvdimm(struct device *dev);
 bool is_cxl_nvdimm(struct device *dev);
 int devm_cxl_add_nvdimm(struct device *host, struct cxl_port *port,
diff --git a/drivers/cxl/pmem.c b/drivers/cxl/pmem.c
index e197883690ef..714beaf1704b 100644
--- a/drivers/cxl/pmem.c
+++ b/drivers/cxl/pmem.c
@@ -13,6 +13,20 @@
 
 static __read_mostly DECLARE_BITMAP(exclusive_cmds, CXL_MEM_COMMAND_ID_MAX);
 
+/**
+ * __devm_cxl_add_nvdimm_bridge() - add the root of a LIBNVDIMM topology
+ * @host: platform firmware root device
+ * @port: CXL port at the root of a CXL topology
+ *
+ * Return: bridge device that can host cxl_nvdimm objects
+ */
+struct cxl_nvdimm_bridge *devm_cxl_add_nvdimm_bridge(struct device *host,
+						     struct cxl_port *port)
+{
+	return __devm_cxl_add_nvdimm_bridge(host, port);
+}
+EXPORT_SYMBOL_NS_GPL(devm_cxl_add_nvdimm_bridge, "CXL");
+
 static void clear_exclusive(void *mds)
 {
 	clear_exclusive_cxl_commands(mds, exclusive_cmds);
-- 
2.53.0

[PATCH v3 2/2] cxl: Fix race of nvdimm_bus object when creating nvdimm objects

[Dave Jiang]

Found issue during running of cxl-translate.sh unit test. Adding a 3s
sleep right before the test seems to make the issue reproduce fairly
consistently. The cxl_translate module has dependency on cxl_acpi and
causes orphaned nvdimm objects to reprobe after cxl_acpi is removed.
The nvdimm_bus object is registered by the cxl_nvb object when
cxl_acpi_probe() is called. With the nvdimm_bus object missing,
__nd_device_register() will trigger NULL pointer dereference when
accessing the dev->parent that points to &nvdimm_bus->dev.

[  192.884510] BUG: kernel NULL pointer dereference, address: 000000000000006c
[  192.895383] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS edk2-20250812-19.fc42 08/12/2025
[  192.897721] Workqueue: cxl_port cxl_bus_rescan_queue [cxl_core]
[  192.899459] RIP: 0010:kobject_get+0xc/0x90
[  192.924871] Call Trace:
[  192.925959]  <TASK>
[  192.926976]  ? pm_runtime_init+0xb9/0xe0
[  192.929712]  __nd_device_register.part.0+0x4d/0xc0 [libnvdimm]
[  192.933314]  __nvdimm_create+0x206/0x290 [libnvdimm]
[  192.936662]  cxl_nvdimm_probe+0x119/0x1d0 [cxl_pmem]
[  192.940245]  cxl_bus_probe+0x1a/0x60 [cxl_core]
[  192.943349]  really_probe+0xde/0x380

This patch also relies on the previous change where
devm_cxl_add_nvdimm_bridge() is called from drivers/cxl/pmem.c instead
of drivers/cxl/core.c to ensure the dependency of cxl_acpi on cxl_pmem.

1. Set probe_type of cxl_nvb to PROBE_FORCE_SYNCHRONOUS to ensure the
   driver is probed synchronously when add_device() is called.
2. Add a check in __devm_cxl_add_nvdimm_bridge() to ensure that the
   cxl_nvb driver is attached during cxl_acpi_probe().
3. Take the cxl_root uport_dev lock and the cxl_nvb->dev lock in
   devm_cxl_add_nvdimm() before checking nvdimm_bus is valid.
4. Set cxl_nvdimm flag to CXL_NVD_F_INVALIDATED so cxl_nvdimm_probe()
   will exit with -EBUSY.

The removal of cxl_nvdimm devices should prevent any orphaned devices
from probing once the nvdimm_bus is gone.

Fixes: 21083f51521f ("cxl/pmem: Register 'pmem' / cxl_nvdimm devices")
Signed-off-by: Dave Jiang <dave.jiang@intel.com>

---
v3:
- squash patch 2 and 3 (Dan)
- Remove nvdimm_bus check from cxl_nvdimm driver (Dan)
- Set an invalidated flag for cxl_nvdimm when nvdimm_bus is released. (Dan)
- Create a helper to see if driver is attached. (Dan)
---
 drivers/cxl/core/pmem.c | 27 +++++++++++++++++++++++++++
 drivers/cxl/cxl.h       |  5 +++++
 drivers/cxl/pmem.c      |  8 +++++++-
 3 files changed, 39 insertions(+), 1 deletion(-)

diff --git a/drivers/cxl/core/pmem.c b/drivers/cxl/core/pmem.c
index 7c78344acc6d..375948ec5fed 100644
--- a/drivers/cxl/core/pmem.c
+++ b/drivers/cxl/core/pmem.c
@@ -115,6 +115,15 @@ static void unregister_nvb(void *_cxl_nvb)
 	device_unregister(&cxl_nvb->dev);
 }
 
+static bool cxl_nvdimm_bridge_failed_attach(struct cxl_nvdimm_bridge *cxl_nvb)
+{
+	struct device *dev = &cxl_nvb->dev;
+
+	guard(device)(dev);
+	/* If the device has no driver, then it failed to attach. */
+	return dev->driver == NULL;
+}
+
 struct cxl_nvdimm_bridge *__devm_cxl_add_nvdimm_bridge(struct device *host,
 						       struct cxl_port *port)
 {
@@ -138,6 +147,11 @@ struct cxl_nvdimm_bridge *__devm_cxl_add_nvdimm_bridge(struct device *host,
 	if (rc)
 		goto err;
 
+	if (cxl_nvdimm_bridge_failed_attach(cxl_nvb)) {
+		unregister_nvb(cxl_nvb);
+		return ERR_PTR(-ENODEV);
+	}
+
 	rc = devm_add_action_or_reset(host, unregister_nvb, cxl_nvb);
 	if (rc)
 		return ERR_PTR(rc);
@@ -248,6 +262,19 @@ int devm_cxl_add_nvdimm(struct device *host, struct cxl_port *port,
 	if (!cxl_nvb)
 		return -ENODEV;
 
+	/*
+	 * Take the uport_dev lock to guard against race of nvdimm_bus object.
+	 * cxl_acpi_probe() registers the nvdimm_bus and is done under the
+	 * root port uport_dev lock.
+	 *
+	 * Take the cxl_nvb device lock to ensure that cxl_nvb driver is in a
+	 * consistent state. And the driver registers nvdimm_bus.
+	 */
+	guard(device)(cxl_nvb->port->uport_dev);
+	guard(device)(&cxl_nvb->dev);
+	if (!cxl_nvb->nvdimm_bus)
+		return -ENODEV;
+
 	cxl_nvd = cxl_nvdimm_alloc(cxl_nvb, cxlmd);
 	if (IS_ERR(cxl_nvd)) {
 		rc = PTR_ERR(cxl_nvd);
diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
index f5850800f400..9b947286eb9b 100644
--- a/drivers/cxl/cxl.h
+++ b/drivers/cxl/cxl.h
@@ -574,11 +574,16 @@ struct cxl_nvdimm_bridge {
 
 #define CXL_DEV_ID_LEN 19
 
+enum {
+	CXL_NVD_F_INVALIDATED = 0,
+};
+
 struct cxl_nvdimm {
 	struct device dev;
 	struct cxl_memdev *cxlmd;
 	u8 dev_id[CXL_DEV_ID_LEN]; /* for nvdimm, string of 'serial' */
 	u64 dirty_shutdowns;
+	unsigned long flags;
 };
 
 struct cxl_pmem_region_mapping {
diff --git a/drivers/cxl/pmem.c b/drivers/cxl/pmem.c
index 714beaf1704b..61f7a0b352aa 100644
--- a/drivers/cxl/pmem.c
+++ b/drivers/cxl/pmem.c
@@ -143,6 +143,9 @@ static int cxl_nvdimm_probe(struct device *dev)
 	struct nvdimm *nvdimm;
 	int rc;
 
+	if (test_bit(CXL_NVD_F_INVALIDATED, &cxl_nvd->flags))
+		return -EBUSY;
+
 	set_exclusive_cxl_commands(mds, exclusive_cmds);
 	rc = devm_add_action_or_reset(dev, clear_exclusive, mds);
 	if (rc)
@@ -323,8 +326,10 @@ static int detach_nvdimm(struct device *dev, void *data)
 	scoped_guard(device, dev) {
 		if (dev->driver) {
 			cxl_nvd = to_cxl_nvdimm(dev);
-			if (cxl_nvd->cxlmd && cxl_nvd->cxlmd->cxl_nvb == data)
+			if (cxl_nvd->cxlmd && cxl_nvd->cxlmd->cxl_nvb == data) {
 				release = true;
+				set_bit(CXL_NVD_F_INVALIDATED, &cxl_nvd->flags);
+			}
 		}
 	}
 	if (release)
@@ -367,6 +372,7 @@ static struct cxl_driver cxl_nvdimm_bridge_driver = {
 	.probe = cxl_nvdimm_bridge_probe,
 	.id = CXL_DEVICE_NVDIMM_BRIDGE,
 	.drv = {
+		.probe_type = PROBE_FORCE_SYNCHRONOUS,
 		.suppress_bind_attrs = true,
 	},
 };
-- 
2.53.0

Re: [PATCH v3 1/2] cxl: Move devm_cxl_add_nvdimm_bridge() to cxl_pmem.ko

[kernel test robot]

Hi Dave,

kernel test robot noticed the following build warnings:

[auto build test WARNING on 63fbf275fa9f18f7020fb8acf54fa107e51d0f23]

url:    https://github.com/intel-lab-lkp/linux/commits/Dave-Jiang/cxl-Move-devm_cxl_add_nvdimm_bridge-to-cxl_pmem-ko/20260214-064242
base:   63fbf275fa9f18f7020fb8acf54fa107e51d0f23
patch link:    https://lore.kernel.org/r/20260213224038.549798-2-dave.jiang%40intel.com
patch subject: [PATCH v3 1/2] cxl: Move devm_cxl_add_nvdimm_bridge() to cxl_pmem.ko
config: powerpc64-randconfig-002-20260214 (https://download.01.org/0day-ci/archive/20260214/202602141202.umHQ46td-lkp@intel.com/config)
compiler: clang version 22.0.0git (https://github.com/llvm/llvm-project 9b8addffa70cee5b2acc5454712d9cf78ce45710)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260214/202602141202.umHQ46td-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202602141202.umHQ46td-lkp@intel.com/

All warnings (new ones prefixed by >>):

>> Warning: drivers/cxl/pmem.c:24 expecting prototype for __devm_cxl_add_nvdimm_bridge(). Prototype was for devm_cxl_add_nvdimm_bridge() instead

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

Re: [PATCH v3 1/2] cxl: Move devm_cxl_add_nvdimm_bridge() to cxl_pmem.ko

[kernel test robot]

Hi Dave,

kernel test robot noticed the following build warnings:

[auto build test WARNING on 63fbf275fa9f18f7020fb8acf54fa107e51d0f23]

url:    https://github.com/intel-lab-lkp/linux/commits/Dave-Jiang/cxl-Move-devm_cxl_add_nvdimm_bridge-to-cxl_pmem-ko/20260214-064242
base:   63fbf275fa9f18f7020fb8acf54fa107e51d0f23
patch link:    https://lore.kernel.org/r/20260213224038.549798-2-dave.jiang%40intel.com
patch subject: [PATCH v3 1/2] cxl: Move devm_cxl_add_nvdimm_bridge() to cxl_pmem.ko
config: x86_64-rhel-9.4 (https://download.01.org/0day-ci/archive/20260214/202602140526.9iCVGQmM-lkp@intel.com/config)
compiler: gcc-14 (Debian 14.2.0-19) 14.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260214/202602140526.9iCVGQmM-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202602140526.9iCVGQmM-lkp@intel.com/

All warnings (new ones prefixed by >>):

>> Warning: drivers/cxl/pmem.c:24 expecting prototype for __devm_cxl_add_nvdimm_bridge(). Prototype was for devm_cxl_add_nvdimm_bridge() instead

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

Re: [PATCH v3 2/2] cxl: Fix race of nvdimm_bus object when creating nvdimm objects

[Gregory Price]

On Fri, Feb 13, 2026 at 03:40:38PM -0700, Dave Jiang wrote:
> @@ -248,6 +262,19 @@ int devm_cxl_add_nvdimm(struct device *host, struct cxl_port *port,
>  	if (!cxl_nvb)
>  		return -ENODEV;
>  
> +	/*
> +	 * Take the uport_dev lock to guard against race of nvdimm_bus object.
> +	 * cxl_acpi_probe() registers the nvdimm_bus and is done under the
> +	 * root port uport_dev lock.
> +	 *
> +	 * Take the cxl_nvb device lock to ensure that cxl_nvb driver is in a
> +	 * consistent state. And the driver registers nvdimm_bus.
> +	 */
> +	guard(device)(cxl_nvb->port->uport_dev);
> +	guard(device)(&cxl_nvb->dev);
> +	if (!cxl_nvb->nvdimm_bus)
> +		return -ENODEV;
> +

I think this leaks the reference on cxl_nvb taken by 

	devm_cxl_add_nvdimm()
		device_find_child()

Maybe:
     if (!cxl_nvb->nvdimm_bus) {
             rc = -ENODEV;
             goto err_alloc;
     }


Reported-by: kreview-0811365

~Gregory

Re: [PATCH v3 0/2] cxl: Fix nvdimm_bus race for nvdimm devices

[Dave Jiang]

On 2/13/26 3:40 PM, Dave Jiang wrote:
> v3:
> - Just move the symbol of devm_cxl_add_nvdimm_bridge() with a wrapper function. (Dan)
> - Squash the functionality of patch 2 and 3. (Dan)
> - Introduce a flag to invalidate cxl_nvdimm when releasing nvdimm_bus. (Dan)
> - With cxl_nvdimm marked as "invalidated" no need the check in cxl_nvdimm_driver. (Dan)

Applied to cxl/fixes
16fb82cadd63 cxl: Fix race of nvdimm_bus object when creating nvdimm objects
e7e222ad73d9 cxl: Move devm_cxl_add_nvdimm_bridge() to cxl_pmem.ko

> 
> v2:
> - Try a different approach
> 
> A small series to address a race for nvdimm_bus object when using the
> nvdimm_bridge object.
> 
> Dave Jiang (2):
>   cxl: Move devm_cxl_add_nvdimm_bridge() to cxl_pmem.ko
>   cxl: Fix race of nvdimm_bus object when creating nvdimm objects
> 
>  drivers/cxl/core/pmem.c | 40 ++++++++++++++++++++++++++++++----------
>  drivers/cxl/cxl.h       |  7 +++++++
>  drivers/cxl/pmem.c      | 22 +++++++++++++++++++++-
>  3 files changed, 58 insertions(+), 11 deletions(-)
> 
> 
> base-commit: 63fbf275fa9f18f7020fb8acf54fa107e51d0f23

Re: [PATCH v3 2/2] cxl: Fix race of nvdimm_bus object when creating nvdimm objects

[Dave Jiang]

On 2/23/26 3:18 PM, Gregory Price wrote:
> On Fri, Feb 13, 2026 at 03:40:38PM -0700, Dave Jiang wrote:
>> @@ -248,6 +262,19 @@ int devm_cxl_add_nvdimm(struct device *host, struct cxl_port *port,
>>  	if (!cxl_nvb)
>>  		return -ENODEV;
>>  
>> +	/*
>> +	 * Take the uport_dev lock to guard against race of nvdimm_bus object.
>> +	 * cxl_acpi_probe() registers the nvdimm_bus and is done under the
>> +	 * root port uport_dev lock.
>> +	 *
>> +	 * Take the cxl_nvb device lock to ensure that cxl_nvb driver is in a
>> +	 * consistent state. And the driver registers nvdimm_bus.
>> +	 */
>> +	guard(device)(cxl_nvb->port->uport_dev);
>> +	guard(device)(&cxl_nvb->dev);
>> +	if (!cxl_nvb->nvdimm_bus)
>> +		return -ENODEV;
>> +
> 
> I think this leaks the reference on cxl_nvb taken by 
> 
> 	devm_cxl_add_nvdimm()
> 		device_find_child()
> 
> Maybe:
>      if (!cxl_nvb->nvdimm_bus) {
>              rc = -ENODEV;
>              goto err_alloc;
>      }
> 
> 
> Reported-by: kreview-0811365

Thanks! I've fixed it up in place in cxl/fixes.

> 
> ~Gregory