[PATCH] acpi, nfit: fix register dimm error handling

[Toshi Kani <toshi.kani@hpe.com>]

A NULL pointer reference kernel bug was observed when
acpi_nfit_add_dimm() called in acpi_nfit_register_dimms()
failed. This error path does not set nfit_mem->nvdimm, but
the 2nd list_for_each_entry() loop in the function assumes
it's always set. Add a check to nfit_mem->nvdimm.

Signed-off-by: Toshi Kani <toshi.kani@hpe.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
---
 drivers/acpi/nfit/core.c |    3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/acpi/nfit/core.c b/drivers/acpi/nfit/core.c
index abeb4df4f22e..b28ce440a06f 100644
--- a/drivers/acpi/nfit/core.c
+++ b/drivers/acpi/nfit/core.c
@@ -1867,6 +1867,9 @@ static int acpi_nfit_register_dimms(struct acpi_nfit_desc *acpi_desc)
 		struct kernfs_node *nfit_kernfs;
 
 		nvdimm = nfit_mem->nvdimm;
+		if (!nvdimm)
+			continue;
+
 		nfit_kernfs = sysfs_get_dirent(nvdimm_kobj(nvdimm)->sd, "nfit");
 		if (nfit_kernfs)
 			nfit_mem->flags_attr = sysfs_get_dirent(nfit_kernfs,