From 96a1fd0d84b17360840f344826897fa71049870e Mon Sep 17 00:00:00 2001 From: Dave Jiang Date: Thu, 12 Feb 2026 14:50:38 -0700 Subject: [PATCH] cxl: Fix race of nvdimm_bus object when creating nvdimm objects 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] [ 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 Fixes: 8fdcb1704f61 ("cxl/pmem: Add initial infrastructure for pmem support") Tested-by: Alison Schofield Reviewed-by: Alison Schofield Link: https://patch.msgid.link/20260205001633.1813643-3-dave.jiang@intel.com Signed-off-by: Dave Jiang --- 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 b652e3486038..68462e38a977 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 +262,21 @@ 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) { + 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 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 c67b30b516bf..082ec0f1c3a0 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, }, };