libnvdimm/security: Require nvdimm_security_setup_events() to succeed

The following warning:

ACPI0012:00: security event setup failed: -19

...is meant to capture exceptional failures of sysfs_get_dirent(),
however it will also fail in the common case when security support is
disabled. A few issues:

1/ A dev_warn() report for a common case is too chatty
2/ The setup of this notifier is generic, no need for it to be driven
from the nfit driver, it can exist completely in the core.
3/ If it fails for any reason besides security support being disabled,
that's fatal and should abort DIMM activation. Userspace may hang if
it never gets overwrite notifications.
4/ The dirent needs to be released.

Move the call to the core 'dimm' driver, make it conditional on security
support being active, make it fatal for the exceptional case, add the
missing sysfs_put() at device disable time.

Fixes: 7d988097c546 ("...Add security DSM overwrite support")
Reviewed-by: Dave Jiang <[e-mail]>
Signed-off-by: Dan Williams <[e-mail]>

drivers/acpi/nfit/core.c

···
 		if (!nvdimm)
 			continue;
 
-		rc = nvdimm_security_setup_events(nvdimm);
-		if (rc < 0)
-			dev_warn(acpi_desc->dev,
-				"security event setup failed: %d\n", rc);
-
 		nfit_kernfs = sysfs_get_dirent(nvdimm_kobj(nvdimm)->sd, "nfit");
 		if (nfit_kernfs)
 			nfit_mem->flags_attr = sysfs_get_dirent(nfit_kernfs,

drivers/nvdimm/dimm.c

···
 	struct nvdimm_drvdata *ndd;
 	int rc;
 
+	rc = nvdimm_security_setup_events(dev);
+	if (rc < 0) {
+		dev_err(dev, "security event setup failed: %d\n", rc);
+		return rc;
+	}
+
 	rc = nvdimm_check_config_data(dev);
 	if (rc) {
 		/* not required for non-aliased nvdimm, ex. NVDIMM-N */

drivers/nvdimm/dimm_devs.c

···
 }
 EXPORT_SYMBOL_GPL(__nvdimm_create);
 
-int nvdimm_security_setup_events(struct nvdimm *nvdimm)
+static void shutdown_security_notify(void *data)
 {
-	nvdimm->sec.overwrite_state = sysfs_get_dirent(nvdimm->dev.kobj.sd,
-			"security");
+	struct nvdimm *nvdimm = data;
+
+	sysfs_put(nvdimm->sec.overwrite_state);
+}
+
+int nvdimm_security_setup_events(struct device *dev)
+{
+	struct nvdimm *nvdimm = to_nvdimm(dev);
+
+	if (nvdimm->sec.state < 0 || !nvdimm->sec.ops
+			|| !nvdimm->sec.ops->overwrite)
+		return 0;
+	nvdimm->sec.overwrite_state = sysfs_get_dirent(dev->kobj.sd, "security");
 	if (!nvdimm->sec.overwrite_state)
-		return -ENODEV;
-	return 0;
+		return -ENOMEM;
+
+	return devm_add_action_or_reset(dev, shutdown_security_notify, nvdimm);
 }
 EXPORT_SYMBOL_GPL(nvdimm_security_setup_events);
 

drivers/nvdimm/nd.h

···
 void nvdimm_set_aliasing(struct device *dev);
 void nvdimm_set_locked(struct device *dev);
 void nvdimm_clear_locked(struct device *dev);
+int nvdimm_security_setup_events(struct device *dev);
 #if IS_ENABLED(CONFIG_NVDIMM_KEYS)
 int nvdimm_security_unlock(struct device *dev);
 #else

include/linux/libnvdimm.h

···
 			cmd_mask, num_flush, flush_wpq, NULL, NULL);
 }
 
-int nvdimm_security_setup_events(struct nvdimm *nvdimm);
 const struct nd_cmd_desc *nd_cmd_dimm_desc(int cmd);
 const struct nd_cmd_desc *nd_cmd_bus_desc(int cmd);
 u32 nd_cmd_in_size(struct nvdimm *nvdimm, int cmd,