acpi, nfit: Further restrict userspace ARS start requests

In addition to not allowing ARS start while the background thread is
actively running, prevent ARS start while any scrub request is pending.

This aligns the window for ARS start submission with the status of ARS
reported via sysfs. Previously userspace could sneak its own ARS start
requests in while sysfs reported -EBUSY.
Reviewed-by: NDave Jiang <dave.jiang@intel.com>
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

drivers/acpi/nfit/core.c

@@ -3341,6 +3341,8 @@ static int acpi_nfit_clear_to_send(struct nvdimm_bus_descriptor *nd_desc,
 		struct nvdimm *nvdimm, unsigned int cmd)
 {
 	struct acpi_nfit_desc *acpi_desc = to_acpi_nfit_desc(nd_desc);
+	struct nfit_spa *nfit_spa;
+	int rc = 0;
 
 	if (nvdimm)
 		return 0;
@@ -3350,13 +3352,20 @@ static int acpi_nfit_clear_to_send(struct nvdimm_bus_descriptor *nd_desc,
 	/*
 	 * The kernel and userspace may race to initiate a scrub, but
 	 * the scrub thread is prepared to lose that initial race.  It
-	 * just needs guarantees that any ars it initiates are not
-	 * interrupted by any intervening start reqeusts from userspace.
+	 * just needs guarantees that any ARS it initiates are not
+	 * interrupted by any intervening start requests from userspace.
 	 */
-	if (work_busy(&acpi_desc->dwork.work))
-		return -EBUSY;
+	mutex_lock(&acpi_desc->init_mutex);
+	list_for_each_entry(nfit_spa, &acpi_desc->spas, list)
+		if (acpi_desc->scrub_spa
+				|| test_bit(ARS_REQ_SHORT, &nfit_spa->ars_state)
+				|| test_bit(ARS_REQ_LONG, &nfit_spa->ars_state)) {
+			rc = -EBUSY;
+			break;
+		}
+	mutex_unlock(&acpi_desc->init_mutex);
 
-	return 0;
+	return rc;
 }
 
 int acpi_nfit_ars_rescan(struct acpi_nfit_desc *acpi_desc,