Check for unlinked znodes after igrab()

The changes in commit 41e1aa2 / PR #9583 introduced a regression on
tmpfile_001_pos: fsetxattr() on a O_TMPFILE file descriptor started
to fail with errno ENODATA:

    openat(AT_FDCWD, "/test", O_RDWR|O_TMPFILE, 0666) = 3
    <...>
    fsetxattr(3, "user.test", <...>, 64, 0) = -1 ENODATA

The originally proposed change on PR #9583 is not susceptible to it,
so just move the code/if-checks around back in that way, to fix it.

Reviewed-by: Pavel Snajdr <snajpa@snajpa.net>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Original-patch-by: Heitor Alves de Siqueira <halves@canonical.com>
Signed-off-by: Mauricio Faria de Oliveira <mfo@canonical.com>
Closes #9602

module/zfs/zfs_znode.c

@@ -1094,7 +1094,8 @@ zfs_zget(zfsvfs_t *zfsvfs, uint64_t obj_num, znode_t **zpp)
 		ASSERT3U(zp->z_id, ==, obj_num);
 		/*
 		 * If zp->z_unlinked is set, the znode is already marked
-		 * for deletion and should not be discovered.
+		 * for deletion and should not be discovered. Check this
+		 * after checking igrab() due to fsetxattr() & O_TMPFILE.
 		 *
 		 * If igrab() returns NULL the VFS has independently
 		 * determined the inode should be evicted and has
@@ -1109,10 +1110,11 @@ zfs_zget(zfsvfs_t *zfsvfs, uint64_t obj_num, znode_t **zpp)
 		 * need to detect the active SA hold thereby informing
 		 * the VFS that this inode should not be evicted.
 		 */
-		if (zp->z_unlinked) {
-			err = SET_ERROR(ENOENT);
-		} else if (igrab(ZTOI(zp)) == NULL) {
-			err = SET_ERROR(EAGAIN);
+		if (igrab(ZTOI(zp)) == NULL) {
+			if (zp->z_unlinked)
+				err = SET_ERROR(ENOENT);
+			else
+				err = SET_ERROR(EAGAIN);
 		} else {
 			*zpp = zp;
 			err = 0;