This is a note to let you know that I've just added the patch titled cxl/pmem: Fix nvdimm registration races to the 6.1-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: cxl-pmem-fix-nvdimm-registration-races.patch and it can be found in the queue-6.1 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From f57aec443c24d2e8e1f3b5b4856aea12ddda4254 Mon Sep 17 00:00:00 2001 From: Dan Williams <dan.j.williams@xxxxxxxxx> Date: Mon, 13 Feb 2023 17:01:05 -0800 Subject: cxl/pmem: Fix nvdimm registration races From: Dan Williams <dan.j.williams@xxxxxxxxx> commit f57aec443c24d2e8e1f3b5b4856aea12ddda4254 upstream. A loop of the form: while true; do modprobe cxl_pci; modprobe -r cxl_pci; done ...fails with the following crash signature: BUG: kernel NULL pointer dereference, address: 0000000000000040 [..] RIP: 0010:cxl_internal_send_cmd+0x5/0xb0 [cxl_core] [..] Call Trace: <TASK> cxl_pmem_ctl+0x121/0x240 [cxl_pmem] nvdimm_get_config_data+0xd6/0x1a0 [libnvdimm] nd_label_data_init+0x135/0x7e0 [libnvdimm] nvdimm_probe+0xd6/0x1c0 [libnvdimm] nvdimm_bus_probe+0x7a/0x1e0 [libnvdimm] really_probe+0xde/0x380 __driver_probe_device+0x78/0x170 driver_probe_device+0x1f/0x90 __device_attach_driver+0x85/0x110 bus_for_each_drv+0x7d/0xc0 __device_attach+0xb4/0x1e0 bus_probe_device+0x9f/0xc0 device_add+0x445/0x9c0 nd_async_device_register+0xe/0x40 [libnvdimm] async_run_entry_fn+0x30/0x130 ...namely that the bottom half of async nvdimm device registration runs after the CXL has already torn down the context that cxl_pmem_ctl() needs. Unlike the ACPI NFIT case that benefits from launching multiple nvdimm device registrations in parallel from those listed in the table, CXL is already marked PROBE_PREFER_ASYNCHRONOUS. So provide for a synchronous registration path to preclude this scenario. Fixes: 21083f51521f ("cxl/pmem: Register 'pmem' / cxl_nvdimm devices") Cc: <stable@xxxxxxxxxxxxxxx> Reported-by: Dave Jiang <dave.jiang@xxxxxxxxx> Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- drivers/cxl/pmem.c | 1 + drivers/nvdimm/bus.c | 19 ++++++++++++++++--- drivers/nvdimm/dimm_devs.c | 5 ++++- drivers/nvdimm/nd-core.h | 1 + include/linux/libnvdimm.h | 3 +++ 5 files changed, 25 insertions(+), 4 deletions(-) --- a/drivers/cxl/pmem.c +++ b/drivers/cxl/pmem.c @@ -75,6 +75,7 @@ static int cxl_nvdimm_probe(struct devic goto out; set_bit(NDD_LABELING, &flags); + set_bit(NDD_REGISTER_SYNC, &flags); set_bit(ND_CMD_GET_CONFIG_SIZE, &cmd_mask); set_bit(ND_CMD_GET_CONFIG_DATA, &cmd_mask); set_bit(ND_CMD_SET_CONFIG_DATA, &cmd_mask); --- a/drivers/nvdimm/bus.c +++ b/drivers/nvdimm/bus.c @@ -508,7 +508,7 @@ static void nd_async_device_unregister(v put_device(dev); } -void nd_device_register(struct device *dev) +static void __nd_device_register(struct device *dev, bool sync) { if (!dev) return; @@ -531,11 +531,24 @@ void nd_device_register(struct device *d } get_device(dev); - async_schedule_dev_domain(nd_async_device_register, dev, - &nd_async_domain); + if (sync) + nd_async_device_register(dev, 0); + else + async_schedule_dev_domain(nd_async_device_register, dev, + &nd_async_domain); +} + +void nd_device_register(struct device *dev) +{ + __nd_device_register(dev, false); } EXPORT_SYMBOL(nd_device_register); +void nd_device_register_sync(struct device *dev) +{ + __nd_device_register(dev, true); +} + void nd_device_unregister(struct device *dev, enum nd_async_mode mode) { bool killed; --- a/drivers/nvdimm/dimm_devs.c +++ b/drivers/nvdimm/dimm_devs.c @@ -617,7 +617,10 @@ struct nvdimm *__nvdimm_create(struct nv nvdimm->sec.ext_flags = nvdimm_security_flags(nvdimm, NVDIMM_MASTER); device_initialize(dev); lockdep_set_class(&dev->mutex, &nvdimm_key); - nd_device_register(dev); + if (test_bit(NDD_REGISTER_SYNC, &flags)) + nd_device_register_sync(dev); + else + nd_device_register(dev); return nvdimm; } --- a/drivers/nvdimm/nd-core.h +++ b/drivers/nvdimm/nd-core.h @@ -107,6 +107,7 @@ int nvdimm_bus_create_ndctl(struct nvdim void nvdimm_bus_destroy_ndctl(struct nvdimm_bus *nvdimm_bus); void nd_synchronize(void); void nd_device_register(struct device *dev); +void nd_device_register_sync(struct device *dev); struct nd_label_id; char *nd_label_gen_id(struct nd_label_id *label_id, const uuid_t *uuid, u32 flags); --- a/include/linux/libnvdimm.h +++ b/include/linux/libnvdimm.h @@ -36,6 +36,9 @@ enum { /* dimm supports namespace labels */ NDD_LABELING = 6, + /* dimm provider wants synchronous registration by __nvdimm_create() */ + NDD_REGISTER_SYNC = 8, + /* need to set a limit somewhere, but yes, this is likely overkill */ ND_IOCTL_MAX_BUFLEN = SZ_4M, ND_CMD_MAX_ELEM = 5, Patches currently in stable-queue which might be from dan.j.williams@xxxxxxxxx are queue-6.1/dax-kmem-fix-leak-of-memory-hotplug-resources.patch queue-6.1/cxl-pmem-fix-nvdimm-registration-races.patch