nvme: don't rely on the changed namespace list log

Don't optimize our namespace rescan based on the changed namespace list
log page as userspace might have changed the content through reading
it.
Suggested-by: NKeith Busch <keith.busch@linux.intel.com>
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NKeith Busch <keith.busch@linux.intel.com>
Reviewed-by: NHannes Reinecke <hare@suse.com>

drivers/nvme/host/core.c

@@ -3197,40 +3197,28 @@ static void nvme_scan_ns_sequential(struct nvme_ctrl *ctrl, unsigned nn)
 	nvme_remove_invalid_namespaces(ctrl, nn);
 }
 
-static bool nvme_scan_changed_ns_log(struct nvme_ctrl *ctrl)
+static void nvme_clear_changed_ns_log(struct nvme_ctrl *ctrl)
 {
 	size_t log_size = NVME_MAX_CHANGED_NAMESPACES * sizeof(__le32);
 	__le32 *log;
-	int error, i;
-	bool ret = false;
+	int error;
 
 	log = kzalloc(log_size, GFP_KERNEL);
 	if (!log)
-		return false;
+		return;
 
+	/*
+	 * We need to read the log to clear the AEN, but we don't want to rely
+	 * on it for the changed namespace information as userspace could have
+	 * raced with us in reading the log page, which could cause us to miss
+	 * updates.
+	 */
 	error = nvme_get_log(ctrl, NVME_LOG_CHANGED_NS, log, log_size);
-	if (error) {
+	if (error)
 		dev_warn(ctrl->device,
 			"reading changed ns log failed: %d\n", error);
-		goto out_free_log;
-	}
-
-	if (log[0] == cpu_to_le32(0xffffffff))
-		goto out_free_log;
 
-	for (i = 0; i < NVME_MAX_CHANGED_NAMESPACES; i++) {
-		u32 nsid = le32_to_cpu(log[i]);
-
-		if (nsid == 0)
-			break;
-		dev_info(ctrl->device, "rescanning namespace %d.\n", nsid);
-		nvme_validate_ns(ctrl, nsid);
-	}
-	ret = true;
-
-out_free_log:
 	kfree(log);
-	return ret;
 }
 
 static void nvme_scan_work(struct work_struct *work)
@@ -3246,9 +3234,8 @@ static void nvme_scan_work(struct work_struct *work)
 	WARN_ON_ONCE(!ctrl->tagset);
 
 	if (test_and_clear_bit(NVME_AER_NOTICE_NS_CHANGED, &ctrl->events)) {
-		if (nvme_scan_changed_ns_log(ctrl))
-			goto out_sort_namespaces;
 		dev_info(ctrl->device, "rescanning namespaces.\n");
+		nvme_clear_changed_ns_log(ctrl);
 	}
 
 	if (nvme_identify_ctrl(ctrl, &id))
@@ -3263,7 +3250,6 @@ static void nvme_scan_work(struct work_struct *work)
 	nvme_scan_ns_sequential(ctrl, nn);
 out_free_id:
 	kfree(id);
-out_sort_namespaces:
 	down_write(&ctrl->namespaces_rwsem);
 	list_sort(NULL, &ctrl->namespaces, ns_cmp);
 	up_write(&ctrl->namespaces_rwsem);