cifs: do not skip link targets when an I/O fails

When I/O fails in one of the currently connected DFS targets, retry it
from other targets as specified in MS-DFSC "3.1.5.2 I/O Operation to
+Target Fails with an Error Other Than STATUS_PATH_NOT_COVERED."

Signed-off-by: Paulo Alcantara (SUSE) <pc@cjr.nz>
Cc: stable@vger.kernel.org
Signed-off-by: Steve French <stfrench@microsoft.com>

Author: Paulo Alcantara

fs/cifs/connect.c

@@ -3513,6 +3513,9 @@ static int connect_dfs_target(struct mount_ctx *mnt_ctx, const char *full_path,
 	struct cifs_sb_info *cifs_sb = mnt_ctx->cifs_sb;
 	char *oldmnt = cifs_sb->ctx->mount_options;
 
+	cifs_dbg(FYI, "%s: full_path=%s ref_path=%s target=%s\n", __func__, full_path, ref_path,
+		 dfs_cache_get_tgt_name(tit));
+
 	rc = dfs_cache_get_tgt_referral(ref_path, tit, &ref);
 	if (rc)
 		goto out;
@@ -3611,13 +3614,18 @@ static int __follow_dfs_link(struct mount_ctx *mnt_ctx)
 	if (rc)
 		goto out;
 
-	/* Try all dfs link targets */
+	/* Try all dfs link targets.  If an I/O fails from currently connected DFS target with an
+	 * error other than STATUS_PATH_NOT_COVERED (-EREMOTE), then retry it from other targets as
+	 * specified in MS-DFSC "3.1.5.2 I/O Operation to Target Fails with an Error Other Than
+	 * STATUS_PATH_NOT_COVERED."
+	 */
 	for (rc = -ENOENT, tit = dfs_cache_get_tgt_iterator(&tl);
 	     tit; tit = dfs_cache_get_next_tgt(&tl, tit)) {
 		rc = connect_dfs_target(mnt_ctx, full_path, mnt_ctx->leaf_fullpath + 1, tit);
 		if (!rc) {
 			rc = is_path_remote(mnt_ctx);
-			break;
+			if (!rc || rc == -EREMOTE)
+				break;
 		}
 	}
 
@@ -3691,7 +3699,7 @@ int cifs_mount(struct cifs_sb_info *cifs_sb, struct smb3_fs_context *ctx)
 		goto error;
 
 	rc = is_path_remote(&mnt_ctx);
-	if (rc == -EREMOTE)
+	if (rc)
 		rc = follow_dfs_link(&mnt_ctx);
 	if (rc)
 		goto error;