OpenZFS 7301 - zpool export -f should be able to interrupt file freeing

Authored by: Alek Pinchuk <alek@nexenta.com>
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: Sanjay Nadkarni <sanjay.nadkarni@nexenta.com>
Reviewed by: Saso Kiselkov <saso.kiselkov@nexenta.com>
Reviewed by: John Kennedy <john.kennedy@delphix.com>
Approved by: Gordon Ross <gordon.ross@nexenta.com>
Reviewed-by: Tim Chase <tim@chase2k.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Ported-by: George Melikov <mail@gmelikov.ru>

OpenZFS-issue: https://www.illumos.org/issues/7301
OpenZFS-commit: https://github.com/openzfs/openzfs/commit/eb72182
Closes #5680

include/sys/zfs_znode.h

@@ -21,6 +21,7 @@
 /*
  * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
  * Copyright (c) 2012, 2015 by Delphix. All rights reserved.
+ * Copyright 2016 Nexenta Systems, Inc. All rights reserved.
  */
 
 #ifndef	_SYS_FS_ZFS_ZNODE_H
@@ -311,6 +312,7 @@ extern int	zfs_sync(struct super_block *, int, cred_t *);
 extern dev_t	zfs_cmpldev(uint64_t);
 extern int	zfs_get_zplprop(objset_t *os, zfs_prop_t prop, uint64_t *value);
 extern int	zfs_get_stats(objset_t *os, nvlist_t *nv);
+extern boolean_t zfs_get_vfs_flag_unmounted(objset_t *os);
 extern void	zfs_znode_dmu_fini(znode_t *);
 extern int	zfs_inode_alloc(struct super_block *, struct inode **ip);
 extern void	zfs_inode_destroy(struct inode *);

module/zfs/dmu.c

@@ -23,7 +23,7 @@
  * Copyright (c) 2011, 2016 by Delphix. All rights reserved.
  * Copyright (c) 2013 by Saso Kiselkov. All rights reserved.
  * Copyright (c) 2013, Joyent, Inc. All rights reserved.
- * Copyright (c) 2014, Nexenta Systems, Inc. All rights reserved.
+ * Copyright (c) 2016, Nexenta Systems, Inc. All rights reserved.
  * Copyright (c) 2015 by Chunwei Chen. All rights reserved.
  */
 
@@ -705,6 +705,22 @@ get_next_chunk(dnode_t *dn, uint64_t *start, uint64_t minimum)
 	return (0);
 }
 
+/*
+ * If this objset is of type OST_ZFS return true if vfs's unmounted flag is set,
+ * otherwise return false.
+ * Used below in dmu_free_long_range_impl() to enable abort when unmounting
+ */
+/*ARGSUSED*/
+static boolean_t
+dmu_objset_zfs_unmounting(objset_t *os)
+{
+#ifdef _KERNEL
+	if (dmu_objset_type(os) == DMU_OST_ZFS)
+		return (zfs_get_vfs_flag_unmounted(os));
+#endif
+	return (B_FALSE);
+}
+
 static int
 dmu_free_long_range_impl(objset_t *os, dnode_t *dn, uint64_t offset,
     uint64_t length)
@@ -726,6 +742,9 @@ dmu_free_long_range_impl(objset_t *os, dnode_t *dn, uint64_t offset,
 		uint64_t chunk_end, chunk_begin;
 		dmu_tx_t *tx;
 
+		if (dmu_objset_zfs_unmounting(dn->dn_objset))
+			return (SET_ERROR(EINTR));
+
 		chunk_end = chunk_begin = offset + length;
 
 		/* move chunk_begin backwards to the beginning of this chunk */

module/zfs/zfs_dir.c

@@ -644,8 +644,8 @@ zfs_rmnode(znode_t *zp)
 		error = dmu_free_long_range(os, zp->z_id, 0, DMU_OBJECT_END);
 		if (error) {
 			/*
-			 * Not enough space.  Leave the file in the unlinked
+			 * Not enough space or we were interrupted by unmount.
-			 * set.
+			 * Leave the file in the unlinked set.
 			 */
 			zfs_znode_dmu_fini(zp);
 			return;

module/zfs/zfs_vfsops.c

@@ -1263,7 +1263,7 @@ EXPORT_SYMBOL(zfs_sb_prune);
 /*
  * Teardown the zfs_sb_t.
  *
- * Note, if 'unmounting' if FALSE, we return with the 'z_teardown_lock'
+ * Note, if 'unmounting' is FALSE, we return with the 'z_teardown_lock'
  * and 'z_teardown_inactive_lock' held.
  */
 int
@@ -1358,8 +1358,8 @@ zfs_sb_teardown(zfs_sb_t *zsb, boolean_t unmounting)
 	 */
 	if (unmounting) {
 		zsb->z_unmounted = B_TRUE;
-		rrm_exit(&zsb->z_teardown_lock, FTAG);
 		rw_exit(&zsb->z_teardown_inactive_lock);
+		rrm_exit(&zsb->z_teardown_lock, FTAG);
 	}
 
 	/*
@@ -1906,6 +1906,28 @@ zfs_get_zplprop(objset_t *os, zfs_prop_t prop, uint64_t *value)
 }
 EXPORT_SYMBOL(zfs_get_zplprop);
 
+/*
+ * Return true if the coresponding vfs's unmounted flag is set.
+ * Otherwise return false.
+ * If this function returns true we know VFS unmount has been initiated.
+ */
+boolean_t
+zfs_get_vfs_flag_unmounted(objset_t *os)
+{
+	zfs_sb_t *zfvp;
+	boolean_t unmounted = B_FALSE;
+
+	ASSERT(dmu_objset_type(os) == DMU_OST_ZFS);
+
+	mutex_enter(&os->os_user_ptr_lock);
+	zfvp = dmu_objset_get_user(os);
+	if (zfvp != NULL && zfvp->z_unmounted)
+		unmounted = B_TRUE;
+	mutex_exit(&os->os_user_ptr_lock);
+
+	return (unmounted);
+}
+
 void
 zfs_init(void)
 {