Dan Williams wrote:
> 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 cxlmd_release_nvdimm() 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: <[email protected]>
> Reported-by: Dave Jiang <[email protected]>
Reviewed-by: Ira Weiny <[email protected]>
> Tested-by: Dave Jiang <[email protected]>
> Signed-off-by: Dan Williams <[email protected]>
> ---
> 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(-)
>
> diff --git a/drivers/cxl/pmem.c b/drivers/cxl/pmem.c
> index 08bbbac9a6d0..71cfa1fdf902 100644
> --- a/drivers/cxl/pmem.c
> +++ b/drivers/cxl/pmem.c
> @@ -76,6 +76,7 @@ static int cxl_nvdimm_probe(struct device *dev)
> return rc;
>
> 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);
> diff --git a/drivers/nvdimm/bus.c b/drivers/nvdimm/bus.c
> index b38d0355b0ac..5ad49056921b 100644
> --- a/drivers/nvdimm/bus.c
> +++ b/drivers/nvdimm/bus.c
> @@ -508,7 +508,7 @@ static void nd_async_device_unregister(void *d,
> async_cookie_t cookie)
> 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 *dev)
> }
> 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;
> diff --git a/drivers/nvdimm/dimm_devs.c b/drivers/nvdimm/dimm_devs.c
> index 1fc081dcf631..6d3b03a9fa02 100644
> --- a/drivers/nvdimm/dimm_devs.c
> +++ b/drivers/nvdimm/dimm_devs.c
> @@ -624,7 +624,10 @@ struct nvdimm *__nvdimm_create(struct nvdimm_bus
> *nvdimm_bus,
> 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;
> }
> diff --git a/drivers/nvdimm/nd-core.h b/drivers/nvdimm/nd-core.h
> index cc86ee09d7c0..845408f10655 100644
> --- a/drivers/nvdimm/nd-core.h
> +++ b/drivers/nvdimm/nd-core.h
> @@ -107,6 +107,7 @@ int nvdimm_bus_create_ndctl(struct nvdimm_bus
> *nvdimm_bus);
> 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);
> diff --git a/include/linux/libnvdimm.h b/include/linux/libnvdimm.h
> index af38252ad704..e772aae71843 100644
> --- a/include/linux/libnvdimm.h
> +++ b/include/linux/libnvdimm.h
> @@ -41,6 +41,9 @@ enum {
> */
> NDD_INCOHERENT = 7,
>
> + /* 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,
>
>
