Linux: syncfs(2) should sync all open files

While debugging problem with data not being synced on umount, we've
noticed that even syncfs(2) doesn't help to get the data written
out. It is because it doesn't actually sync any of the live znodes.

Signed-off-by: Pavel Snajdr <[email protected]>

module/os/linux/zfs/zfs_vfsops.c

@@ -1551,12 +1551,12 @@ zfs_preumount(struct super_block *sb)
 	/* zfsvfs is NULL when zfs_domount fails during mount */
 	if (zfsvfs) {
 		/*
-		* Since we have to disable zpl_prune_sb when umounting,
-		* because the shrinker gets freed before zpl_kill_sb is
-		* ever called, the umount might be unable to sync open files.
-		*
-		* Let's do it here.
-		*/
+		 * Since we have to disable zpl_prune_sb when umounting,
+		 * because the shrinker gets freed before zpl_kill_sb is
+		 * ever called, the umount might be unable to sync open files.
+		 *
+		 * Let's do it here.
+		 */
 		mutex_enter(&zfsvfs->z_znodes_lock);
 		list_for_each_entry(zp, &zfsvfs->z_all_znodes, z_link_node) {
 			if (zp->z_sa_hdl)

module/os/linux/zfs/zpl_super.c

@@ -109,11 +109,23 @@ zpl_sync_fs(struct super_block *sb, int wait)
 {
 	fstrans_cookie_t cookie;
 	cred_t *cr = CRED();
+	znode_t *zp;
+	zfsvfs_t *zfsvfs = sb->s_fs_info;
 	int error;
 
 	crhold(cr);
 	cookie = spl_fstrans_mark();
-	error = -zfs_sync(sb, wait, cr);
+	mutex_enter(&zfsvfs->z_znodes_lock);
+	for (zp = list_head(&zfsvfs->z_all_znodes); zp;
+	    zp = list_next(&zfsvfs->z_all_znodes, zp)) {
+		if (zp->z_sa_hdl)
+			error = -zfs_fsync(zp, wait, cr);
+		if (error != 0)
+			break;
+	}
+	mutex_exit(&zfsvfs->z_znodes_lock);
+	if (error == 0)
+		error = -zfs_sync(sb, wait, cr);
 	spl_fstrans_unmark(cookie);
 	crfree(cr);
 	ASSERT3S(error, <=, 0);