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

Dave Jiang
2026-02-13T22:40:43Z

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