libnvdimm/security: ensure sysfs poll thread woke up and fetch updated attr

commit 7d988097c5 ("acpi/nfit, libnvdimm/security: Add security DSM overwrite support")
adds a sysfs_notify_dirent() to wake up userspace poll thread when the "overwrite"
operation has completed. But the notification is issued before the internal
dimm security state and flags have been updated, so the userspace poll thread
wakes up and fetches the not-yet-updated attr and falls back to sleep, forever.
But if user from another terminal issue "ndctl wait-overwrite nmemX" again,
the command returns instantly.

Link: https://lore.kernel.org/r/1596494499-9852-3-git-send-email-jane.chu@oracle.com
Fixes: 7d988097c5 ("acpi/nfit, libnvdimm/security: Add security DSM overwrite support")
Cc: Dave Jiang <dave.jiang@intel.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Signed-off-by: Jane Chu <jane.chu@oracle.com>
Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>

drivers/nvdimm/security.c

@@ -450,14 +450,19 @@ void __nvdimm_security_overwrite_query(struct nvdimm *nvdimm)
 	else
 		dev_dbg(&nvdimm->dev, "overwrite completed\n");
 
-	if (nvdimm->sec.overwrite_state)
-		sysfs_notify_dirent(nvdimm->sec.overwrite_state);
+	/*
+	 * Mark the overwrite work done and update dimm security flags,
+	 * then send a sysfs event notification to wake up userspace
+	 * poll threads to picked up the changed state.
+	 */
 	nvdimm->sec.overwrite_tmo = 0;
 	clear_bit(NDD_SECURITY_OVERWRITE, &nvdimm->flags);
 	clear_bit(NDD_WORK_PENDING, &nvdimm->flags);
-	put_device(&nvdimm->dev);
 	nvdimm->sec.flags = nvdimm_security_flags(nvdimm, NVDIMM_USER);
 	nvdimm->sec.ext_flags = nvdimm_security_flags(nvdimm, NVDIMM_MASTER);
+	if (nvdimm->sec.overwrite_state)
+		sysfs_notify_dirent(nvdimm->sec.overwrite_state);
+	put_device(&nvdimm->dev);
 }
 
 void nvdimm_security_overwrite_query(struct work_struct *work)