Revert "Fix unlink/xattr deadlock"

This reverts commit b00131d43ca344d4b205a03ab3eb771a060e5087 which
is no longer needed due to e89260a1c8851ce05ea04b23606ba438b271d890.

This change forces all xattr znodes to hold a reference on their
parent which ensures prune_icache() will never attempt to evict
both the parent and child concurrently.  This effectively prevents
the deadlock condition from ever occuring.

Therefore we can safely revert back to the upstream synchronous
cleanup code.  This is nice because it keeps our code base closer
to upstream and resolves the performance issues introduced by the
original deadlock fix.

Signed-off-by: Brian Behlendorf <[email protected]>
Closes #457

2 files changed, 55 insertions, 90 deletions

diff --git a/module/zfs/zfs_dir.c b/module/zfs/zfs_dir.c
index 670e31398..a373537dd 100644
--- a/module/zfs/zfs_dir.c
+++ b/module/zfs/zfs_dir.c
@@ -483,6 +483,57 @@ zfs_unlinked_add(znode_t *zp, dmu_tx_t *tx)
 }
 
 /*
+ * Clean up any znodes that had no links when we either crashed or
+ * (force) umounted the file system.
+ */
+void
+zfs_unlinked_drain(zfs_sb_t *zsb)
+{
+	zap_cursor_t	zc;
+	zap_attribute_t zap;
+	dmu_object_info_t doi;
+	znode_t		*zp;
+	int		error;
+
+	/*
+	 * Interate over the contents of the unlinked set.
+	 */
+	for (zap_cursor_init(&zc, zsb->z_os, zsb->z_unlinkedobj);
+	    zap_cursor_retrieve(&zc, &zap) == 0;
+	    zap_cursor_advance(&zc)) {
+
+		/*
+		 * See what kind of object we have in list
+		 */
+
+		error = dmu_object_info(zsb->z_os, zap.za_first_integer, &doi);
+		if (error != 0)
+			continue;
+
+		ASSERT((doi.doi_type == DMU_OT_PLAIN_FILE_CONTENTS) ||
+		    (doi.doi_type == DMU_OT_DIRECTORY_CONTENTS));
+		/*
+		 * We need to re-mark these list entries for deletion,
+		 * so we pull them back into core and set zp->z_unlinked.
+		 */
+		error = zfs_zget(zsb, zap.za_first_integer, &zp);
+
+		/*
+		 * We may pick up znodes that are already marked for deletion.
+		 * This could happen during the purge of an extended attribute
+		 * directory.  All we need to do is skip over them, since they
+		 * are already in the system marked z_unlinked.
+		 */
+		if (error != 0)
+			continue;
+
+		zp->z_unlinked = B_TRUE;
+		iput(ZTOI(zp));
+	}
+	zap_cursor_fini(&zc);
+}
+
+/*
  * Delete the entire contents of a directory.  Return a count
  * of the number of entries that could not be deleted. If we encounter
  * an error, return a count of at least one so that the directory stays
@@ -548,71 +599,6 @@ zfs_purgedir(znode_t *dzp)
 	return (skipped);
 }
 
-/*
- * Clean up any znodes that had no links when we either crashed or
- * (force) umounted the file system.
- */
-void
-zfs_unlinked_drain(zfs_sb_t *zsb)
-{
-	zap_cursor_t	zc;
-	zap_attribute_t zap;
-	dmu_object_info_t doi;
-	znode_t		*zp;
-	int		error;
-
-	/*
-	 * Interate over the contents of the unlinked set.
-	 */
-	for (zap_cursor_init(&zc, zsb->z_os, zsb->z_unlinkedobj);
-	    zap_cursor_retrieve(&zc, &zap) == 0;
-	    zap_cursor_advance(&zc)) {
-
-		/*
-		 * See what kind of object we have in list
-		 */
-
-		error = dmu_object_info(zsb->z_os, zap.za_first_integer, &doi);
-		if (error != 0)
-			continue;
-
-		ASSERT((doi.doi_type == DMU_OT_PLAIN_FILE_CONTENTS) ||
-		    (doi.doi_type == DMU_OT_DIRECTORY_CONTENTS));
-		/*
-		 * We need to re-mark these list entries for deletion,
-		 * so we pull them back into core and set zp->z_unlinked.
-		 */
-		error = zfs_zget(zsb, zap.za_first_integer, &zp);
-
-		/*
-		 * We may pick up znodes that are already marked for deletion.
-		 * This could happen during the purge of an extended attribute
-		 * directory.  All we need to do is skip over them, since they
-		 * are already in the system marked z_unlinked.
-		 */
-		if (error != 0)
-			continue;
-
-		zp->z_unlinked = B_TRUE;
-
-		/*
-		 * If this is an attribute directory, purge its contents.
-		 */
-		if (S_ISDIR(ZTOI(zp)->i_mode) && (zp->z_pflags & ZFS_XATTR)) {
-			/*
-			 * We don't need to check the return value of
-			 * zfs_purgedir here, because zfs_rmnode will just
-			 * return this xattr directory to the unlinked set
-			 * until all of its xattrs are gone.
-			 */
-			(void) zfs_purgedir(zp);
-		}
-
-		iput(ZTOI(zp));
-	}
-	zap_cursor_fini(&zc);
-}
-
 void
 zfs_rmnode(znode_t *zp)
 {
@@ -622,7 +608,6 @@ zfs_rmnode(znode_t *zp)
 	dmu_tx_t	*tx;
 	uint64_t	acl_obj;
 	uint64_t	xattr_obj;
-	uint64_t	count;
 	int		error;
 
 	ASSERT(zp->z_links == 0);
@@ -632,27 +617,13 @@ zfs_rmnode(znode_t *zp)
 	 * If this is an attribute directory, purge its contents.
 	 */
 	if (S_ISDIR(ZTOI(zp)->i_mode) && (zp->z_pflags & ZFS_XATTR)) {
-		error = zap_count(os, zp->z_id, &count);
-		if (error) {
-			zfs_znode_dmu_fini(zp);
-			return;
-		}
-
-		if (count > 0) {
-			taskq_t *taskq;
-
+		if (zfs_purgedir(zp) != 0) {
 			/*
-			 * There are still directory entries in this xattr
-			 * directory.  Let zfs_unlinked_drain() deal with
-			 * them to avoid deadlocking this process in the
-			 * zfs_purgedir()->zfs_zget()->ilookup() callpath
-			 * on the xattr inode's I_FREEING bit.
+			 * Not enough space to delete some xattrs.
+			 * Leave it in the unlinked set.
 			 */
-			taskq = dsl_pool_iput_taskq(dmu_objset_pool(os));
-			taskq_dispatch(taskq, (task_func_t *)
-			    zfs_unlinked_drain, zsb, TQ_SLEEP);
-
 			zfs_znode_dmu_fini(zp);
+
 			return;
 		}
 	}
diff --git a/module/zfs/zfs_vfsops.c b/module/zfs/zfs_vfsops.c
index 90f9055af..175dca821 100644
--- a/module/zfs/zfs_vfsops.c
+++ b/module/zfs/zfs_vfsops.c
@@ -1041,12 +1041,6 @@ zfs_sb_teardown(zfs_sb_t *zsb, boolean_t unmounting)
 	}
 
 	/*
-	 * Drain the iput_taskq to ensure all active references to the
-	 * zfs_sb_t have been handled only then can it be safely destroyed.
-	 */
-	taskq_wait(dsl_pool_iput_taskq(dmu_objset_pool(zsb->z_os)));
-
-	/*
 	 * Close the zil. NB: Can't close the zil while zfs_inactive
 	 * threads are blocked as zil_close can call zfs_inactive.
 	 */