[PATCH 6.18 034/314] cxl: Fix race of nvdimm_bus object when creating nvdimm objects

Sasha Levin
2026-03-10T11:25:11Z

From: Dave Jiang <dave.jiang@intel.com>

[ Upstream commit 96a1fd0d84b17360840f344826897fa71049870e ]

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.

[ dj: Fixed 0-day reported kdoc issue. ]
[ dj: Fix cxl_nvb reference leak on error. Gregory (kreview-0811365) ]

Suggested-by: Dan Williams <dan.j.williams@intel.com>
Fixes: 8fdcb1704f61 ("cxl/pmem: Add initial infrastructure for pmem support")
Tested-by: Alison Schofield <alison.schofield@intel.com>
Reviewed-by: Alison Schofield <alison.schofield@intel.com?>
Link: https://patch.msgid.link/20260205001633.1813643-3-dave.jiang@intel.com
Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/cxl/core/pmem.c | 29 +++++++++++++++++++++++++++++
drivers/cxl/cxl.h | 5 +++++
drivers/cxl/pmem.c | 10 ++++++++--
3 files changed, 42 insertions(+), 2 deletions(-)

diff --git a/drivers/cxl/core/pmem.c b/drivers/cxl/core/pmem.c
index e1325936183a6..e3a8b8d813333 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);
@@ -247,6 +261,21 @@ int devm_cxl_add_nvdimm(struct cxl_port *parent_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) {
+ rc = -ENODEV;
+ goto err_alloc;
+ }
+
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 443296da74db1..3a794278cc7fe 100644
--- a/drivers/cxl/cxl.h
+++ b/drivers/cxl/cxl.h
@@ -555,11 +555,16 @@ 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 714beaf1704be..c00b84b960761 100644
--- a/drivers/cxl/pmem.c
+++ b/drivers/cxl/pmem.c
@@ -14,7 +14,7 @@
static __read_mostly DECLARE_BITMAP(exclusive_cmds, CXL_MEM_COMMAND_ID_MAX);

/**
- * __devm_cxl_add_nvdimm_bridge() - add the root of a LIBNVDIMM topology
+ * 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
*
@@ -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,
},
};
--
2.51.0