When a region is disabled, there is no driver attached. Therefore
dev->driverdata is NULL. An attempt to write to regionN/deep_flush via sysfs
would cause a NULL pointer dereference. Bail when dev->driver is NULL to
protect this scenario.

Fix: ab630891ce0eb(libnvdimm, region: sysfs trigger for nvdimm_flush())

Signed-off-by: Dave Jiang <dave.ji...@intel.com>
 drivers/nvdimm/region_devs.c |    4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/nvdimm/region_devs.c b/drivers/nvdimm/region_devs.c
index a612be6f019d..d5619b7feb6a 100644
--- a/drivers/nvdimm/region_devs.c
+++ b/drivers/nvdimm/region_devs.c
@@ -1074,6 +1074,10 @@ void nvdimm_flush(struct nd_region *nd_region)
        struct nd_region_data *ndrd = dev_get_drvdata(&nd_region->dev);
        int i, idx;
+       /* protect against disabled region */
+       if (!nd_region->dev.driver)
+               return;
         * Try to encourage some diversity in flush hint addresses
         * across cpus assuming a limited number of flush hints.

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