[PATCH 0/8][v2] Cleanup how we handle root refs, part 2

[PATCH 0/8][v2] Cleanup how we handle root refs, part 2

[Josef Bacik]

v1->v2:
- Rebased onto latest misc-next.
- Fixed a problem where we were dropping the ino_cache_inode in the final put of
  the root, which is braindead since it was holding a ref on that root.

--------------- Original email -------------------
This series depends on part 1 and is the final bit of cleaning up how we handle
root refs.  Historically the ref counting has been just about kfree'ing the root
itself and not actually cleaning up the root and free'ing it.  This makes it
sort of awkward to handle the lifetime of a root, as we will just free a bunch
of things related to the root, but then not free the actual root until we drop
the last reference.

This patch series brings the actual cleanup of the root inside the ref
accounting for the root.  In addition to that we also now hold refs on the root
for all of the various users of the root in order to make the lifetime more
coherent.  Previously if you looked up a root we just held it in memory until
unmount and then we had to do two put's to clear it out.  Now we hold refs to
the root when we open an inode in the root, so we could get rid of this extra
ref holding.  Now we hold refs for discrete operations, like putting it in the
radix tree, adding to the dead roots list, and of course opening an inode.

This final piece allows us to remove the subvol_srcu, which was the reason for
all of this work.  I fixed the original deadlock, but it's use was sporadic and
inconsistent, which is a recipe for trouble.

Unfortunately I was not able to kill the per-root inode rb tree yet.  We use it
in relocation to drop the extent cache for extents we are relocating, and
there's not a very clear way to accomplish that without the inode rbtree right
now.  However this work means that once I've fixed that problem we can delete
the inode rbtree completely.  Thanks,

Josef

[PATCH 1/8] btrfs: make the extent buffer leak check per fs info

[Josef Bacik]

I'm going to make the entire destruction of btrfs_root's controlled by
their refcount, so it will be helpful to notice if we're leaking their
eb's on umount.

Signed-off-by: Josef Bacik <josef@toxicpanda.com>
---
 fs/btrfs/ctree.h     |  3 +++
 fs/btrfs/disk-io.c   |  3 +++
 fs/btrfs/extent_io.c | 45 ++++++++++++++++++++++----------------------
 fs/btrfs/extent_io.h |  7 +++++++
 4 files changed, 36 insertions(+), 22 deletions(-)

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 6006e10f371f..acda509aee46 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -950,6 +950,9 @@ struct btrfs_fs_info {
 	struct kobject *debug_kobj;
 	struct kobject *discard_debug_kobj;
 	struct list_head alloced_roots;
+
+	spinlock_t eb_leak_lock;
+	struct list_head alloced_ebs;
 #endif
 };
 
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 62067f60456e..514cd8725def 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1576,6 +1576,7 @@ void btrfs_free_fs_info(struct btrfs_fs_info *fs_info)
 	btrfs_put_root(fs_info->free_space_root);
 	btrfs_put_root(fs_info->fs_root);
 	btrfs_check_leaked_roots(fs_info);
+	btrfs_extent_buffer_leak_debug_check(fs_info);
 	kfree(fs_info->super_copy);
 	kfree(fs_info->super_for_commit);
 	kvfree(fs_info);
@@ -2705,6 +2706,8 @@ void btrfs_init_fs_info(struct btrfs_fs_info *fs_info)
 	INIT_LIST_HEAD(&fs_info->unused_bgs);
 #ifdef CONFIG_BTRFS_DEBUG
 	INIT_LIST_HEAD(&fs_info->alloced_roots);
+	INIT_LIST_HEAD(&fs_info->alloced_ebs);
+	spin_lock_init(&fs_info->eb_leak_lock);
 #endif
 	extent_map_tree_init(&fs_info->mapping_tree);
 	btrfs_init_block_rsv(&fs_info->global_block_rsv,
diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index e2d30287e2d5..f4411e6cc753 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -35,42 +35,45 @@ static inline bool extent_state_in_tree(const struct extent_state *state)
 }
 
 #ifdef CONFIG_BTRFS_DEBUG
-static LIST_HEAD(buffers);
 static LIST_HEAD(states);
-
 static DEFINE_SPINLOCK(leak_lock);
 
-static inline
-void btrfs_leak_debug_add(struct list_head *new, struct list_head *head)
+static inline void btrfs_leak_debug_add(spinlock_t *lock,
+					struct list_head *new,
+					struct list_head *head)
 {
 	unsigned long flags;
 
-	spin_lock_irqsave(&leak_lock, flags);
+	spin_lock_irqsave(lock, flags);
 	list_add(new, head);
-	spin_unlock_irqrestore(&leak_lock, flags);
+	spin_unlock_irqrestore(lock, flags);
 }
 
-static inline
-void btrfs_leak_debug_del(struct list_head *entry)
+static inline void btrfs_leak_debug_del(spinlock_t *lock,
+					struct list_head *entry)
 {
 	unsigned long flags;
 
-	spin_lock_irqsave(&leak_lock, flags);
+	spin_lock_irqsave(lock, flags);
 	list_del(entry);
-	spin_unlock_irqrestore(&leak_lock, flags);
+	spin_unlock_irqrestore(lock, flags);
 }
 
-static inline void btrfs_extent_buffer_leak_debug_check(void)
+void btrfs_extent_buffer_leak_debug_check(struct btrfs_fs_info *fs_info)
 {
 	struct extent_buffer *eb;
+	unsigned long flags;
 
-	while (!list_empty(&buffers)) {
-		eb = list_entry(buffers.next, struct extent_buffer, leak_list);
+	spin_lock_irqsave(&fs_info->eb_leak_lock, flags);
+	while (!list_empty(&fs_info->alloced_ebs)) {
+		eb = list_first_entry(&fs_info->alloced_ebs,
+				      struct extent_buffer, leak_list);
 		pr_err("BTRFS: buffer leak start %llu len %lu refs %d bflags %lu\n",
 		       eb->start, eb->len, atomic_read(&eb->refs), eb->bflags);
 		list_del(&eb->leak_list);
 		kmem_cache_free(extent_buffer_cache, eb);
 	}
+	spin_unlock_irqrestore(&fs_info->eb_leak_lock, flags);
 }
 
 static inline void btrfs_extent_state_leak_debug_check(void)
@@ -107,9 +110,8 @@ static inline void __btrfs_debug_check_extent_io_range(const char *caller,
 	}
 }
 #else
-#define btrfs_leak_debug_add(new, head)	do {} while (0)
-#define btrfs_leak_debug_del(entry)	do {} while (0)
-#define btrfs_extent_buffer_leak_debug_check()	do {} while (0)
+#define btrfs_leak_debug_add(lock, new, head)	do {} while (0)
+#define btrfs_leak_debug_del(lock, entry)	do {} while (0)
 #define btrfs_extent_state_leak_debug_check()	do {} while (0)
 #define btrfs_debug_check_extent_io_range(c, s, e)	do {} while (0)
 #endif
@@ -246,8 +248,6 @@ void __cold extent_state_cache_exit(void)
 
 void __cold extent_io_exit(void)
 {
-	btrfs_extent_buffer_leak_debug_check();
-
 	/*
 	 * Make sure all delayed rcu free are flushed before we
 	 * destroy caches.
@@ -314,7 +314,7 @@ static struct extent_state *alloc_extent_state(gfp_t mask)
 	state->state = 0;
 	state->failrec = NULL;
 	RB_CLEAR_NODE(&state->rb_node);
-	btrfs_leak_debug_add(&state->leak_list, &states);
+	btrfs_leak_debug_add(&leak_lock, &state->leak_list, &states);
 	refcount_set(&state->refs, 1);
 	init_waitqueue_head(&state->wq);
 	trace_alloc_extent_state(state, mask, _RET_IP_);
@@ -327,7 +327,7 @@ void free_extent_state(struct extent_state *state)
 		return;
 	if (refcount_dec_and_test(&state->refs)) {
 		WARN_ON(extent_state_in_tree(state));
-		btrfs_leak_debug_del(&state->leak_list);
+		btrfs_leak_debug_del(&leak_lock, &state->leak_list);
 		trace_free_extent_state(state, _RET_IP_);
 		kmem_cache_free(extent_state_cache, state);
 	}
@@ -4787,7 +4787,7 @@ int extent_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
 
 static void __free_extent_buffer(struct extent_buffer *eb)
 {
-	btrfs_leak_debug_del(&eb->leak_list);
+	btrfs_leak_debug_del(&eb->fs_info->eb_leak_lock, &eb->leak_list);
 	kmem_cache_free(extent_buffer_cache, eb);
 }
 
@@ -4874,7 +4874,8 @@ __alloc_extent_buffer(struct btrfs_fs_info *fs_info, u64 start,
 	init_waitqueue_head(&eb->write_lock_wq);
 	init_waitqueue_head(&eb->read_lock_wq);
 
-	btrfs_leak_debug_add(&eb->leak_list, &buffers);
+	btrfs_leak_debug_add(&fs_info->eb_leak_lock, &eb->leak_list,
+			     &fs_info->alloced_ebs);
 
 	spin_lock_init(&eb->refs_lock);
 	atomic_set(&eb->refs, 1);
diff --git a/fs/btrfs/extent_io.h b/fs/btrfs/extent_io.h
index 5d205bbaafdc..199bb3e3fe18 100644
--- a/fs/btrfs/extent_io.h
+++ b/fs/btrfs/extent_io.h
@@ -325,4 +325,11 @@ bool find_lock_delalloc_range(struct inode *inode,
 #endif
 struct extent_buffer *alloc_test_extent_buffer(struct btrfs_fs_info *fs_info,
 					       u64 start);
+
+#ifdef CONFIG_BTRFS_DEBUG
+void btrfs_extent_buffer_leak_debug_check(struct btrfs_fs_info *fs_info);
+#else
+#define btrfs_extent_buffer_leak_debug_check(fs_info)	do {} while (0)
+#endif
+
 #endif
-- 
2.24.1

[PATCH 2/8] btrfs: move ino_cache_inode dropping

[Josef Bacik]

We are going to make root life be controlled soley by refcounting, and
inodes will be one of the things that hold a ref on the root.  This
means we need to handle dropping the ino_cache_inode outside of the root
freeing logic, so move it into btrfs_drop_and_free_fs_root() so it is
cleaned up properly on unmount.

Signed-off-by: Josef Bacik <josef@toxicpanda.com>
---
 fs/btrfs/disk-io.c     | 5 ++++-
 fs/btrfs/transaction.c | 4 ++++
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 514cd8725def..6f6742805729 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -3905,12 +3905,15 @@ void btrfs_drop_and_free_fs_root(struct btrfs_fs_info *fs_info,
 		__btrfs_remove_free_space_cache(root->free_ino_pinned);
 	if (root->free_ino_ctl)
 		__btrfs_remove_free_space_cache(root->free_ino_ctl);
+	if (root->ino_cache_inode) {
+		iput(root->ino_cache_inode);
+		root->ino_cache_inode = NULL;
+	}
 	btrfs_free_fs_root(root);
 }
 
 void btrfs_free_fs_root(struct btrfs_root *root)
 {
-	iput(root->ino_cache_inode);
 	WARN_ON(!RB_EMPTY_ROOT(&root->inode_tree));
 	if (root->anon_dev)
 		free_anon_bdev(root->anon_dev);
diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index e194d3e4e3a9..c1b34c8c9fd6 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -2424,6 +2424,10 @@ int btrfs_clean_one_deleted_snapshot(struct btrfs_root *root)
 	btrfs_debug(fs_info, "cleaner removing %llu", root->root_key.objectid);
 
 	btrfs_kill_all_delayed_nodes(root);
+	if (root->ino_cache_inode) {
+		iput(root->ino_cache_inode);
+		root->ino_cache_inode = NULL;
+	}
 
 	if (btrfs_header_backref_rev(root->node) <
 			BTRFS_MIXED_BACKREF_REV)
-- 
2.24.1

[PATCH 3/8] btrfs: move the root freeing stuff into btrfs_put_root

[Josef Bacik]

There are a few different ways to free roots, either you allocated them
yourself and you just do

free_extent_buffer(root->node);
free_extent_buffer(root->commit_node);
btrfs_put_root(root);

Which is the pattern for log roots.  Or for snapshots/subvolumes that
are being dropped you simply call btrfs_free_fs_root() which does all
the cleanup for you.

Unify this all into btrfs_put_root(), so that we don't free up things
associated with the root until the last reference is dropped.  This
makes the root freeing code much more significant.

The only caveat is at close_ctree() time we have to free the extent
buffers for all of our main roots (extent_root, chunk_root, etc) because
we have to drop the btree_inode and we'll run into issues if we hold
onto those nodes until ->kill_sb() time.  This will be addressed in the
future when we kill the btree_inode.

Signed-off-by: Josef Bacik <josef@toxicpanda.com>
---
 fs/btrfs/disk-io.c           | 64 ++++++++++++++++++------------------
 fs/btrfs/disk-io.h           | 16 +--------
 fs/btrfs/extent-tree.c       |  7 ++--
 fs/btrfs/extent_io.c         | 16 +++++++--
 fs/btrfs/free-space-tree.c   |  2 --
 fs/btrfs/qgroup.c            |  7 +---
 fs/btrfs/relocation.c        |  4 ---
 fs/btrfs/tests/btrfs-tests.c |  5 +--
 fs/btrfs/tree-log.c          |  6 ----
 9 files changed, 50 insertions(+), 77 deletions(-)

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 6f6742805729..d2a6f6355331 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1304,11 +1304,8 @@ struct btrfs_root *btrfs_create_tree(struct btrfs_trans_handle *trans,
 	return root;
 
 fail:
-	if (leaf) {
+	if (leaf)
 		btrfs_tree_unlock(leaf);
-		free_extent_buffer(root->commit_root);
-		free_extent_buffer(leaf);
-	}
 	btrfs_put_root(root);
 
 	return ERR_PTR(ret);
@@ -1431,10 +1428,10 @@ struct btrfs_root *btrfs_read_tree_root(struct btrfs_root *tree_root,
 				     generation, level, NULL);
 	if (IS_ERR(root->node)) {
 		ret = PTR_ERR(root->node);
+		root->node = NULL;
 		goto find_fail;
 	} else if (!btrfs_buffer_uptodate(root->node, generation, 0)) {
 		ret = -EIO;
-		free_extent_buffer(root->node);
 		goto find_fail;
 	}
 	root->commit_root = btrfs_root_node(root);
@@ -1663,14 +1660,14 @@ struct btrfs_root *btrfs_get_fs_root(struct btrfs_fs_info *fs_info,
 	if (ret) {
 		btrfs_put_root(root);
 		if (ret == -EEXIST) {
-			btrfs_free_fs_root(root);
+			btrfs_put_root(root);
 			goto again;
 		}
 		goto fail;
 	}
 	return root;
 fail:
-	btrfs_free_fs_root(root);
+	btrfs_put_root(root);
 	return ERR_PTR(ret);
 }
 
@@ -2042,11 +2039,35 @@ static void free_root_pointers(struct btrfs_fs_info *info, bool free_chunk_root)
 	free_root_extent_buffers(info->csum_root);
 	free_root_extent_buffers(info->quota_root);
 	free_root_extent_buffers(info->uuid_root);
+	free_root_extent_buffers(info->fs_root);
 	if (free_chunk_root)
 		free_root_extent_buffers(info->chunk_root);
 	free_root_extent_buffers(info->free_space_root);
 }
 
+void btrfs_put_root(struct btrfs_root *root)
+{
+	if (!root)
+		return;
+	if (refcount_dec_and_test(&root->refs)) {
+		WARN_ON(!RB_EMPTY_ROOT(&root->inode_tree));
+		if (root->anon_dev)
+			free_anon_bdev(root->anon_dev);
+		if (root->subv_writers)
+			btrfs_free_subvolume_writers(root->subv_writers);
+		free_extent_buffer(root->node);
+		free_extent_buffer(root->commit_root);
+		kfree(root->free_ino_ctl);
+		kfree(root->free_ino_pinned);
+#ifdef CONFIG_BTRFS_DEBUG
+		spin_lock(&root->fs_info->fs_roots_radix_lock);
+		list_del_init(&root->leak_list);
+		spin_unlock(&root->fs_info->fs_roots_radix_lock);
+#endif
+		kfree(root);
+	}
+}
+
 void btrfs_free_fs_roots(struct btrfs_fs_info *fs_info)
 {
 	int ret;
@@ -2058,13 +2079,10 @@ void btrfs_free_fs_roots(struct btrfs_fs_info *fs_info)
 				     struct btrfs_root, root_list);
 		list_del(&gang[0]->root_list);
 
-		if (test_bit(BTRFS_ROOT_IN_RADIX, &gang[0]->state)) {
+		if (test_bit(BTRFS_ROOT_IN_RADIX, &gang[0]->state))
 			btrfs_drop_and_free_fs_root(fs_info, gang[0]);
-		} else {
-			free_extent_buffer(gang[0]->node);
-			free_extent_buffer(gang[0]->commit_root);
+		else
 			btrfs_put_root(gang[0]);
-		}
 	}
 
 	while (1) {
@@ -2271,11 +2289,11 @@ static int btrfs_replay_log(struct btrfs_fs_info *fs_info,
 	if (IS_ERR(log_tree_root->node)) {
 		btrfs_warn(fs_info, "failed to read log tree");
 		ret = PTR_ERR(log_tree_root->node);
+		log_tree_root->node = NULL;
 		btrfs_put_root(log_tree_root);
 		return ret;
 	} else if (!extent_buffer_uptodate(log_tree_root->node)) {
 		btrfs_err(fs_info, "failed to read log tree");
-		free_extent_buffer(log_tree_root->node);
 		btrfs_put_root(log_tree_root);
 		return -EIO;
 	}
@@ -2284,7 +2302,6 @@ static int btrfs_replay_log(struct btrfs_fs_info *fs_info,
 	if (ret) {
 		btrfs_handle_fs_error(fs_info, ret,
 				      "Failed to recover log tree");
-		free_extent_buffer(log_tree_root->node);
 		btrfs_put_root(log_tree_root);
 		return ret;
 	}
@@ -3894,8 +3911,6 @@ void btrfs_drop_and_free_fs_root(struct btrfs_fs_info *fs_info,
 	if (test_bit(BTRFS_FS_STATE_ERROR, &fs_info->fs_state)) {
 		btrfs_free_log(NULL, root);
 		if (root->reloc_root) {
-			free_extent_buffer(root->reloc_root->node);
-			free_extent_buffer(root->reloc_root->commit_root);
 			btrfs_put_root(root->reloc_root);
 			root->reloc_root = NULL;
 		}
@@ -3909,20 +3924,6 @@ void btrfs_drop_and_free_fs_root(struct btrfs_fs_info *fs_info,
 		iput(root->ino_cache_inode);
 		root->ino_cache_inode = NULL;
 	}
-	btrfs_free_fs_root(root);
-}
-
-void btrfs_free_fs_root(struct btrfs_root *root)
-{
-	WARN_ON(!RB_EMPTY_ROOT(&root->inode_tree));
-	if (root->anon_dev)
-		free_anon_bdev(root->anon_dev);
-	if (root->subv_writers)
-		btrfs_free_subvolume_writers(root->subv_writers);
-	free_extent_buffer(root->node);
-	free_extent_buffer(root->commit_root);
-	kfree(root->free_ino_ctl);
-	kfree(root->free_ino_pinned);
 	btrfs_put_root(root);
 }
 
@@ -4074,8 +4075,6 @@ void __cold close_ctree(struct btrfs_fs_info *fs_info)
 	btrfs_sysfs_remove_mounted(fs_info);
 	btrfs_sysfs_remove_fsid(fs_info->fs_devices);
 
-	btrfs_free_fs_roots(fs_info);
-
 	btrfs_put_block_group_cache(fs_info);
 
 	/*
@@ -4089,6 +4088,7 @@ void __cold close_ctree(struct btrfs_fs_info *fs_info)
 
 	clear_bit(BTRFS_FS_OPEN, &fs_info->flags);
 	free_root_pointers(fs_info, true);
+	btrfs_free_fs_roots(fs_info);
 
 	iput(fs_info->btree_inode);
 
diff --git a/fs/btrfs/disk-io.h b/fs/btrfs/disk-io.h
index db21ab614357..860a9a3bd8d1 100644
--- a/fs/btrfs/disk-io.h
+++ b/fs/btrfs/disk-io.h
@@ -76,7 +76,6 @@ void btrfs_btree_balance_dirty(struct btrfs_fs_info *fs_info);
 void btrfs_btree_balance_dirty_nodelay(struct btrfs_fs_info *fs_info);
 void btrfs_drop_and_free_fs_root(struct btrfs_fs_info *fs_info,
 				 struct btrfs_root *root);
-void btrfs_free_fs_root(struct btrfs_root *root);
 
 #ifdef CONFIG_BTRFS_FS_RUN_SANITY_TESTS
 struct btrfs_root *btrfs_alloc_dummy_root(struct btrfs_fs_info *fs_info);
@@ -98,20 +97,7 @@ static inline struct btrfs_root *btrfs_grab_root(struct btrfs_root *root)
 	return NULL;
 }
 
-static inline void btrfs_put_root(struct btrfs_root *root)
-{
-	if (!root)
-		return;
-	if (refcount_dec_and_test(&root->refs)) {
-#ifdef CONFIG_BTRFS_DEBUG
-		spin_lock(&root->fs_info->fs_roots_radix_lock);
-		list_del_init(&root->leak_list);
-		spin_unlock(&root->fs_info->fs_roots_radix_lock);
-#endif
-		kfree(root);
-	}
-}
-
+void btrfs_put_root(struct btrfs_root *root);
 void btrfs_mark_buffer_dirty(struct extent_buffer *buf);
 int btrfs_buffer_uptodate(struct extent_buffer *buf, u64 parent_transid,
 			  int atomic);
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index c43acb329fa6..0783341ef2e7 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -5411,13 +5411,10 @@ int btrfs_drop_snapshot(struct btrfs_root *root,
 		}
 	}
 
-	if (test_bit(BTRFS_ROOT_IN_RADIX, &root->state)) {
+	if (test_bit(BTRFS_ROOT_IN_RADIX, &root->state))
 		btrfs_add_dropped_root(trans, root);
-	} else {
-		free_extent_buffer(root->node);
-		free_extent_buffer(root->commit_root);
+	else
 		btrfs_put_root(root);
-	}
 	root_dropped = true;
 out_end_trans:
 	btrfs_end_transaction_throttle(trans);
diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index f4411e6cc753..0d40cd7427ba 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -64,12 +64,20 @@ void btrfs_extent_buffer_leak_debug_check(struct btrfs_fs_info *fs_info)
 	struct extent_buffer *eb;
 	unsigned long flags;
 
+	/*
+	 * If we didn't get into open_ctree our alloced_ebs will not be init'ed,
+	 * so just skip this.
+	 */
+	if (fs_info->alloced_ebs.next == NULL)
+		return;
+
 	spin_lock_irqsave(&fs_info->eb_leak_lock, flags);
 	while (!list_empty(&fs_info->alloced_ebs)) {
 		eb = list_first_entry(&fs_info->alloced_ebs,
 				      struct extent_buffer, leak_list);
-		pr_err("BTRFS: buffer leak start %llu len %lu refs %d bflags %lu\n",
-		       eb->start, eb->len, atomic_read(&eb->refs), eb->bflags);
+		pr_err("BTRFS: buffer leak start %llu len %lu refs %d bflags %lu owner %llu\n",
+		       eb->start, eb->len, atomic_read(&eb->refs), eb->bflags,
+		       btrfs_header_owner(eb));
 		list_del(&eb->leak_list);
 		kmem_cache_free(extent_buffer_cache, eb);
 	}
@@ -4787,7 +4795,6 @@ int extent_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
 
 static void __free_extent_buffer(struct extent_buffer *eb)
 {
-	btrfs_leak_debug_del(&eb->fs_info->eb_leak_lock, &eb->leak_list);
 	kmem_cache_free(extent_buffer_cache, eb);
 }
 
@@ -4853,6 +4860,7 @@ static void btrfs_release_extent_buffer_pages(struct extent_buffer *eb)
 static inline void btrfs_release_extent_buffer(struct extent_buffer *eb)
 {
 	btrfs_release_extent_buffer_pages(eb);
+	btrfs_leak_debug_del(&eb->fs_info->eb_leak_lock, &eb->leak_list);
 	__free_extent_buffer(eb);
 }
 
@@ -5240,6 +5248,8 @@ static int release_extent_buffer(struct extent_buffer *eb)
 			spin_unlock(&eb->refs_lock);
 		}
 
+		btrfs_leak_debug_del(&eb->fs_info->eb_leak_lock,
+				     &eb->leak_list);
 		/* Should be safe to release our pages at this point */
 		btrfs_release_extent_buffer_pages(eb);
 #ifdef CONFIG_BTRFS_FS_RUN_SANITY_TESTS
diff --git a/fs/btrfs/free-space-tree.c b/fs/btrfs/free-space-tree.c
index bc43950eb32f..8b1f5c8897b7 100644
--- a/fs/btrfs/free-space-tree.c
+++ b/fs/btrfs/free-space-tree.c
@@ -1251,8 +1251,6 @@ int btrfs_clear_free_space_tree(struct btrfs_fs_info *fs_info)
 	btrfs_free_tree_block(trans, free_space_root, free_space_root->node,
 			      0, 1);
 
-	free_extent_buffer(free_space_root->node);
-	free_extent_buffer(free_space_root->commit_root);
 	btrfs_put_root(free_space_root);
 
 	return btrfs_commit_transaction(trans);
diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
index 6ae868eb9a17..ac192a7696f3 100644
--- a/fs/btrfs/qgroup.c
+++ b/fs/btrfs/qgroup.c
@@ -1037,11 +1037,8 @@ int btrfs_quota_enable(struct btrfs_fs_info *fs_info)
 out_free_path:
 	btrfs_free_path(path);
 out_free_root:
-	if (ret) {
-		free_extent_buffer(quota_root->node);
-		free_extent_buffer(quota_root->commit_root);
+	if (ret)
 		btrfs_put_root(quota_root);
-	}
 out:
 	if (ret) {
 		ulist_free(fs_info->qgroup_ulist);
@@ -1104,8 +1101,6 @@ int btrfs_quota_disable(struct btrfs_fs_info *fs_info)
 	btrfs_tree_unlock(quota_root->node);
 	btrfs_free_tree_block(trans, quota_root, quota_root->node, 0, 1);
 
-	free_extent_buffer(quota_root->node);
-	free_extent_buffer(quota_root->commit_root);
 	btrfs_put_root(quota_root);
 
 end_trans:
diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
index cfbcc6f80ca3..c5d17cc04ed2 100644
--- a/fs/btrfs/relocation.c
+++ b/fs/btrfs/relocation.c
@@ -2503,10 +2503,6 @@ void free_reloc_roots(struct list_head *list)
 		reloc_root = list_entry(list->next, struct btrfs_root,
 					root_list);
 		__del_reloc_root(reloc_root);
-		free_extent_buffer(reloc_root->node);
-		free_extent_buffer(reloc_root->commit_root);
-		reloc_root->node = NULL;
-		reloc_root->commit_root = NULL;
 	}
 }
 
diff --git a/fs/btrfs/tests/btrfs-tests.c b/fs/btrfs/tests/btrfs-tests.c
index 69c9afef06e3..42e62fd2809c 100644
--- a/fs/btrfs/tests/btrfs-tests.c
+++ b/fs/btrfs/tests/btrfs-tests.c
@@ -194,6 +194,7 @@ void btrfs_free_dummy_fs_info(struct btrfs_fs_info *fs_info)
 	cleanup_srcu_struct(&fs_info->subvol_srcu);
 	kfree(fs_info->super_copy);
 	btrfs_check_leaked_roots(fs_info);
+	btrfs_extent_buffer_leak_debug_check(fs_info);
 	kfree(fs_info->fs_devices);
 	kfree(fs_info);
 }
@@ -205,10 +206,6 @@ void btrfs_free_dummy_root(struct btrfs_root *root)
 	/* Will be freed by btrfs_free_fs_roots */
 	if (WARN_ON(test_bit(BTRFS_ROOT_IN_RADIX, &root->state)))
 		return;
-	if (root->node) {
-		/* One for allocate_extent_buffer */
-		free_extent_buffer(root->node);
-	}
 	btrfs_put_root(root);
 }
 
diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c
index e4e53d38cbc1..80978ebfdcbb 100644
--- a/fs/btrfs/tree-log.c
+++ b/fs/btrfs/tree-log.c
@@ -3283,7 +3283,6 @@ static void free_log_tree(struct btrfs_trans_handle *trans,
 
 	clear_extent_bits(&log->dirty_log_pages, 0, (u64)-1,
 			  EXTENT_DIRTY | EXTENT_NEW | EXTENT_NEED_WAIT);
-	free_extent_buffer(log->node);
 	btrfs_put_root(log);
 }
 
@@ -6132,8 +6131,6 @@ int btrfs_recover_log_trees(struct btrfs_root *log_root_tree)
 				ret = btrfs_pin_extent_for_log_replay(fs_info,
 							log->node->start,
 							log->node->len);
-			free_extent_buffer(log->node);
-			free_extent_buffer(log->commit_root);
 			btrfs_put_root(log);
 
 			if (!ret)
@@ -6171,8 +6168,6 @@ int btrfs_recover_log_trees(struct btrfs_root *log_root_tree)
 
 		wc.replay_dest->log_root = NULL;
 		btrfs_put_root(wc.replay_dest);
-		free_extent_buffer(log->node);
-		free_extent_buffer(log->commit_root);
 		btrfs_put_root(log);
 
 		if (ret)
@@ -6204,7 +6199,6 @@ int btrfs_recover_log_trees(struct btrfs_root *log_root_tree)
 	if (ret)
 		return ret;
 
-	free_extent_buffer(log_root_tree->node);
 	log_root_tree->log_root = NULL;
 	clear_bit(BTRFS_FS_LOG_RECOVERING, &fs_info->flags);
 	btrfs_put_root(log_root_tree);
-- 
2.24.1

[PATCH 4/8] btrfs: make inodes hold a ref on their roots

[Josef Bacik]

If we make sure all the inodes have refs on their root we don't have to
worry about the root disappearing while we have open inodes.

Signed-off-by: Josef Bacik <josef@toxicpanda.com>
---
 fs/btrfs/disk-io.c | 2 +-
 fs/btrfs/inode.c   | 8 +++++---
 2 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index d2a6f6355331..ca474f87aba5 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -2144,7 +2144,7 @@ static void btrfs_init_btree_inode(struct btrfs_fs_info *fs_info)
 
 	BTRFS_I(inode)->io_tree.ops = &btree_extent_io_ops;
 
-	BTRFS_I(inode)->root = fs_info->tree_root;
+	BTRFS_I(inode)->root = btrfs_grab_root(fs_info->tree_root);
 	memset(&BTRFS_I(inode)->location, 0, sizeof(struct btrfs_key));
 	set_bit(BTRFS_INODE_DUMMY, &BTRFS_I(inode)->runtime_flags);
 	btrfs_insert_inode_hash(inode);
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index cbbe72d0600b..f7afa44d7cf3 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -5102,7 +5102,8 @@ static int btrfs_init_locked_inode(struct inode *inode, void *p)
 	inode->i_ino = args->location->objectid;
 	memcpy(&BTRFS_I(inode)->location, args->location,
 	       sizeof(*args->location));
-	BTRFS_I(inode)->root = args->root;
+	BTRFS_I(inode)->root = btrfs_grab_root(args->root);
+	BUG_ON(args->root && !BTRFS_I(inode)->root);
 	return 0;
 }
 
@@ -5183,7 +5184,7 @@ static struct inode *new_simple_dir(struct super_block *s,
 	if (!inode)
 		return ERR_PTR(-ENOMEM);
 
-	BTRFS_I(inode)->root = root;
+	BTRFS_I(inode)->root = btrfs_grab_root(root);
 	memcpy(&BTRFS_I(inode)->location, key, sizeof(*key));
 	set_bit(BTRFS_INODE_DUMMY, &BTRFS_I(inode)->runtime_flags);
 
@@ -5751,7 +5752,7 @@ static struct inode *btrfs_new_inode(struct btrfs_trans_handle *trans,
 	 */
 	BTRFS_I(inode)->index_cnt = 2;
 	BTRFS_I(inode)->dir_index = *index;
-	BTRFS_I(inode)->root = root;
+	BTRFS_I(inode)->root = btrfs_grab_root(root);
 	BTRFS_I(inode)->generation = trans->transid;
 	inode->i_generation = BTRFS_I(inode)->generation;
 
@@ -8765,6 +8766,7 @@ void btrfs_destroy_inode(struct inode *inode)
 	btrfs_qgroup_check_reserved_leak(inode);
 	inode_tree_del(inode);
 	btrfs_drop_extent_cache(BTRFS_I(inode), 0, (u64)-1, 0);
+	btrfs_put_root(BTRFS_I(inode)->root);
 }
 
 int btrfs_drop_inode(struct inode *inode)
-- 
2.24.1

[PATCH 5/8] btrfs: hold a ref on the root on the dead roots list

[Josef Bacik]

At the point we add a root to the dead roots list we have no open inodes
for that root, so we need to hold a ref on that root to keep it from
disappearing.

Signed-off-by: Josef Bacik <josef@toxicpanda.com>
---
 fs/btrfs/disk-io.c     | 3 +--
 fs/btrfs/transaction.c | 6 ++++--
 2 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index ca474f87aba5..be9b1a1b1a33 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -2081,8 +2081,7 @@ void btrfs_free_fs_roots(struct btrfs_fs_info *fs_info)
 
 		if (test_bit(BTRFS_ROOT_IN_RADIX, &gang[0]->state))
 			btrfs_drop_and_free_fs_root(fs_info, gang[0]);
-		else
-			btrfs_put_root(gang[0]);
+		btrfs_put_root(gang[0]);
 	}
 
 	while (1) {
diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index c1b34c8c9fd6..27a535d4bb4f 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -1260,8 +1260,10 @@ void btrfs_add_dead_root(struct btrfs_root *root)
 	struct btrfs_fs_info *fs_info = root->fs_info;
 
 	spin_lock(&fs_info->trans_lock);
-	if (list_empty(&root->root_list))
+	if (list_empty(&root->root_list)) {
+		btrfs_grab_root(root);
 		list_add_tail(&root->root_list, &fs_info->dead_roots);
+	}
 	spin_unlock(&fs_info->trans_lock);
 }
 
@@ -2434,7 +2436,7 @@ int btrfs_clean_one_deleted_snapshot(struct btrfs_root *root)
 		ret = btrfs_drop_snapshot(root, NULL, 0, 0);
 	else
 		ret = btrfs_drop_snapshot(root, NULL, 1, 0);
-
+	btrfs_put_root(root);
 	return (ret < 0) ? 0 : 1;
 }
 
-- 
2.24.1

[PATCH 6/8] btrfs: don't take an extra root ref at allocation time

[Josef Bacik]

Now that all the users of roots take references for them we can drop the
extra root ref we've been taking.  Before we had roots at 2 refs for the
life of the file system, one for the radix tree, and one simply for
existing.  Now that we have proper ref accounting in all places that use
roots we can drop this extra ref simply for existing as we no longer
need it.

Signed-off-by: Josef Bacik <josef@toxicpanda.com>
---
 fs/btrfs/disk-io.c            | 20 ++++++--------------
 fs/btrfs/tests/qgroup-tests.c |  2 ++
 2 files changed, 8 insertions(+), 14 deletions(-)

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index be9b1a1b1a33..42f352dfca45 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1647,22 +1647,11 @@ struct btrfs_root *btrfs_get_fs_root(struct btrfs_fs_info *fs_info,
 	if (ret == 0)
 		set_bit(BTRFS_ROOT_ORPHAN_ITEM_INSERTED, &root->state);
 
-	/*
-	 * All roots have two refs on them at all times, one for the mounted fs,
-	 * and one for being in the radix tree.  This way we only free the root
-	 * when we are unmounting or deleting the subvolume.  We get one ref
-	 * from __setup_root, one for inserting it into the radix tree, and then
-	 * we have the third for returning it, and the caller will put it when
-	 * it's done with the root.
-	 */
-	btrfs_grab_root(root);
 	ret = btrfs_insert_fs_root(fs_info, root);
 	if (ret) {
 		btrfs_put_root(root);
-		if (ret == -EEXIST) {
-			btrfs_put_root(root);
+		if (ret == -EEXIST)
 			goto again;
-		}
 		goto fail;
 	}
 	return root;
@@ -3897,11 +3886,13 @@ int write_all_supers(struct btrfs_fs_info *fs_info, int max_mirrors)
 void btrfs_drop_and_free_fs_root(struct btrfs_fs_info *fs_info,
 				  struct btrfs_root *root)
 {
+	bool drop_ref = false;
+
 	spin_lock(&fs_info->fs_roots_radix_lock);
 	radix_tree_delete(&fs_info->fs_roots_radix,
 			  (unsigned long)root->root_key.objectid);
 	if (test_and_clear_bit(BTRFS_ROOT_IN_RADIX, &root->state))
-		btrfs_put_root(root);
+		drop_ref = true;
 	spin_unlock(&fs_info->fs_roots_radix_lock);
 
 	if (btrfs_root_refs(&root->root_item) == 0)
@@ -3923,7 +3914,8 @@ void btrfs_drop_and_free_fs_root(struct btrfs_fs_info *fs_info,
 		iput(root->ino_cache_inode);
 		root->ino_cache_inode = NULL;
 	}
-	btrfs_put_root(root);
+	if (drop_ref)
+		btrfs_put_root(root);
 }
 
 int btrfs_cleanup_fs_roots(struct btrfs_fs_info *fs_info)
diff --git a/fs/btrfs/tests/qgroup-tests.c b/fs/btrfs/tests/qgroup-tests.c
index ac035a6fa003..ce1ca8e73c2d 100644
--- a/fs/btrfs/tests/qgroup-tests.c
+++ b/fs/btrfs/tests/qgroup-tests.c
@@ -507,6 +507,7 @@ int btrfs_test_qgroups(u32 sectorsize, u32 nodesize)
 		test_err("couldn't insert fs root %d", ret);
 		goto out;
 	}
+	btrfs_put_root(tmp_root);
 
 	tmp_root = btrfs_alloc_dummy_root(fs_info);
 	if (IS_ERR(tmp_root)) {
@@ -521,6 +522,7 @@ int btrfs_test_qgroups(u32 sectorsize, u32 nodesize)
 		test_err("couldn't insert fs root %d", ret);
 		goto out;
 	}
+	btrfs_put_root(tmp_root);
 
 	test_msg("running qgroup tests");
 	ret = test_no_shared_qgroup(root, sectorsize, nodesize);
-- 
2.24.1

[PATCH 7/8] btrfs: make btrfs_cleanup_fs_roots use the fs_roots_radix_lock

[Josef Bacik]

The radix root is primarily protected by the fs_roots_radix_lock, so use
that to lookup and get a ref on all of our fs roots in
btrfs_cleanup_fs_roots.

Signed-off-by: Josef Bacik <josef@toxicpanda.com>
---
 fs/btrfs/disk-io.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 42f352dfca45..73479b4bbf34 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -3925,15 +3925,14 @@ int btrfs_cleanup_fs_roots(struct btrfs_fs_info *fs_info)
 	int i = 0;
 	int err = 0;
 	unsigned int ret = 0;
-	int index;
 
 	while (1) {
-		index = srcu_read_lock(&fs_info->subvol_srcu);
+		spin_lock(&fs_info->fs_roots_radix_lock);
 		ret = radix_tree_gang_lookup(&fs_info->fs_roots_radix,
 					     (void **)gang, root_objectid,
 					     ARRAY_SIZE(gang));
 		if (!ret) {
-			srcu_read_unlock(&fs_info->subvol_srcu, index);
+			spin_unlock(&fs_info->fs_roots_radix_lock);
 			break;
 		}
 		root_objectid = gang[ret - 1]->root_key.objectid + 1;
@@ -3947,7 +3946,7 @@ int btrfs_cleanup_fs_roots(struct btrfs_fs_info *fs_info)
 			/* grab all the search result for later use */
 			gang[i] = btrfs_grab_root(gang[i]);
 		}
-		srcu_read_unlock(&fs_info->subvol_srcu, index);
+		spin_unlock(&fs_info->fs_roots_radix_lock);
 
 		for (i = 0; i < ret; i++) {
 			if (!gang[i])
-- 
2.24.1

[PATCH 8/8] btrfs: kill the subvol_srcu

[Josef Bacik]

Now that we have proper root ref counting everywhere we can kill the
subvol_srcu.

Signed-off-by: Josef Bacik <josef@toxicpanda.com>
---
 fs/btrfs/backref.c           | 12 +-----------
 fs/btrfs/ctree.h             |  1 -
 fs/btrfs/disk-io.c           | 37 +++++++++---------------------------
 fs/btrfs/export.c            | 21 ++++----------------
 fs/btrfs/file.c              |  5 -----
 fs/btrfs/inode.c             |  3 ---
 fs/btrfs/send.c              | 14 --------------
 fs/btrfs/tests/btrfs-tests.c |  9 ---------
 8 files changed, 14 insertions(+), 88 deletions(-)

diff --git a/fs/btrfs/backref.c b/fs/btrfs/backref.c
index ded46efac27d..9d0f87df2c35 100644
--- a/fs/btrfs/backref.c
+++ b/fs/btrfs/backref.c
@@ -512,23 +512,18 @@ static int resolve_indirect_ref(struct btrfs_fs_info *fs_info,
 	int ret = 0;
 	int root_level;
 	int level = ref->level;
-	int index;
 
 	root_key.objectid = ref->root_id;
 	root_key.type = BTRFS_ROOT_ITEM_KEY;
 	root_key.offset = (u64)-1;
 
-	index = srcu_read_lock(&fs_info->subvol_srcu);
-
 	root = btrfs_get_fs_root(fs_info, &root_key, false);
 	if (IS_ERR(root)) {
-		srcu_read_unlock(&fs_info->subvol_srcu, index);
 		ret = PTR_ERR(root);
 		goto out_free;
 	}
 
 	if (btrfs_is_testing(fs_info)) {
-		srcu_read_unlock(&fs_info->subvol_srcu, index);
 		ret = -ENOENT;
 		goto out;
 	}
@@ -540,10 +535,8 @@ static int resolve_indirect_ref(struct btrfs_fs_info *fs_info,
 	else
 		root_level = btrfs_old_root_level(root, time_seq);
 
-	if (root_level + 1 == level) {
-		srcu_read_unlock(&fs_info->subvol_srcu, index);
+	if (root_level + 1 == level)
 		goto out;
-	}
 
 	path->lowest_level = level;
 	if (time_seq == SEQ_LAST)
@@ -553,9 +546,6 @@ static int resolve_indirect_ref(struct btrfs_fs_info *fs_info,
 		ret = btrfs_search_old_slot(root, &ref->key_for_search, path,
 					    time_seq);
 
-	/* root node has been locked, we can release @subvol_srcu safely here */
-	srcu_read_unlock(&fs_info->subvol_srcu, index);
-
 	btrfs_debug(fs_info,
 		"search slot in root %llu (level %d, ref count %d) returned %d for key (%llu %u %llu)",
 		 ref->root_id, level, ref->count, ret,
diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index acda509aee46..00cf1641f1b9 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -696,7 +696,6 @@ struct btrfs_fs_info {
 	struct rw_semaphore cleanup_work_sem;
 
 	struct rw_semaphore subvol_sem;
-	struct srcu_struct subvol_srcu;
 
 	spinlock_t trans_lock;
 	/*
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 73479b4bbf34..d453bdc74e91 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -2809,46 +2809,33 @@ static int init_mount_fs_info(struct btrfs_fs_info *fs_info, struct super_block
 	sb->s_blocksize = BTRFS_BDEV_BLOCKSIZE;
 	sb->s_blocksize_bits = blksize_bits(BTRFS_BDEV_BLOCKSIZE);
 
-	ret = init_srcu_struct(&fs_info->subvol_srcu);
-	if (ret)
-		return ret;
-
 	ret = percpu_counter_init(&fs_info->dio_bytes, 0, GFP_KERNEL);
 	if (ret)
-		goto fail;
+		return ret;
 
 	ret = percpu_counter_init(&fs_info->dirty_metadata_bytes, 0, GFP_KERNEL);
 	if (ret)
-		goto fail;
+		return ret;
 
 	fs_info->dirty_metadata_batch = PAGE_SIZE *
 					(1 + ilog2(nr_cpu_ids));
 
 	ret = percpu_counter_init(&fs_info->delalloc_bytes, 0, GFP_KERNEL);
 	if (ret)
-		goto fail;
+		return ret;
 
 	ret = percpu_counter_init(&fs_info->dev_replace.bio_counter, 0,
 			GFP_KERNEL);
 	if (ret)
-		goto fail;
+		return ret;
 
 	fs_info->delayed_root = kmalloc(sizeof(struct btrfs_delayed_root),
 					GFP_KERNEL);
-	if (!fs_info->delayed_root) {
-		ret = -ENOMEM;
-		goto fail;
-	}
+	if (!fs_info->delayed_root)
+		return -ENOMEM;
 	btrfs_init_delayed_root(fs_info->delayed_root);
 
-	ret = btrfs_alloc_stripe_hash_table(fs_info);
-	if (ret)
-		goto fail;
-
-	return 0;
-fail:
-	cleanup_srcu_struct(&fs_info->subvol_srcu);
-	return ret;
+	return btrfs_alloc_stripe_hash_table(fs_info);
 }
 
 int __cold open_ctree(struct super_block *sb,
@@ -2885,13 +2872,13 @@ int __cold open_ctree(struct super_block *sb,
 					BTRFS_CHUNK_TREE_OBJECTID, GFP_KERNEL);
 	if (!tree_root || !chunk_root) {
 		err = -ENOMEM;
-		goto fail_srcu;
+		goto fail;
 	}
 
 	fs_info->btree_inode = new_inode(sb);
 	if (!fs_info->btree_inode) {
 		err = -ENOMEM;
-		goto fail_srcu;
+		goto fail;
 	}
 	mapping_set_gfp_mask(fs_info->btree_inode->i_mapping, GFP_NOFS);
 	btrfs_init_btree_inode(fs_info);
@@ -3399,8 +3386,6 @@ int __cold open_ctree(struct super_block *sb,
 	btrfs_mapping_tree_free(&fs_info->mapping_tree);
 
 	iput(fs_info->btree_inode);
-fail_srcu:
-	cleanup_srcu_struct(&fs_info->subvol_srcu);
 fail:
 	btrfs_close_devices(fs_info->fs_devices);
 	return err;
@@ -3895,9 +3880,6 @@ void btrfs_drop_and_free_fs_root(struct btrfs_fs_info *fs_info,
 		drop_ref = true;
 	spin_unlock(&fs_info->fs_roots_radix_lock);
 
-	if (btrfs_root_refs(&root->root_item) == 0)
-		synchronize_srcu(&fs_info->subvol_srcu);
-
 	if (test_bit(BTRFS_FS_STATE_ERROR, &fs_info->fs_state)) {
 		btrfs_free_log(NULL, root);
 		if (root->reloc_root) {
@@ -4089,7 +4071,6 @@ void __cold close_ctree(struct btrfs_fs_info *fs_info)
 
 	btrfs_mapping_tree_free(&fs_info->mapping_tree);
 	btrfs_close_devices(fs_info->fs_devices);
-	cleanup_srcu_struct(&fs_info->subvol_srcu);
 }
 
 int btrfs_buffer_uptodate(struct extent_buffer *buf, u64 parent_transid,
diff --git a/fs/btrfs/export.c b/fs/btrfs/export.c
index 657fd6ad6e18..7f9dd8384083 100644
--- a/fs/btrfs/export.c
+++ b/fs/btrfs/export.c
@@ -65,8 +65,6 @@ static struct dentry *btrfs_get_dentry(struct super_block *sb, u64 objectid,
 	struct btrfs_root *root;
 	struct inode *inode;
 	struct btrfs_key key;
-	int index;
-	int err = 0;
 
 	if (objectid < BTRFS_FIRST_FREE_OBJECTID)
 		return ERR_PTR(-ESTALE);
@@ -75,13 +73,9 @@ static struct dentry *btrfs_get_dentry(struct super_block *sb, u64 objectid,
 	key.type = BTRFS_ROOT_ITEM_KEY;
 	key.offset = (u64)-1;
 
-	index = srcu_read_lock(&fs_info->subvol_srcu);
-
 	root = btrfs_get_fs_root(fs_info, &key, true);
-	if (IS_ERR(root)) {
-		err = PTR_ERR(root);
-		goto fail;
-	}
+	if (IS_ERR(root))
+		return ERR_CAST(root);
 
 	key.objectid = objectid;
 	key.type = BTRFS_INODE_ITEM_KEY;
@@ -89,12 +83,8 @@ static struct dentry *btrfs_get_dentry(struct super_block *sb, u64 objectid,
 
 	inode = btrfs_iget(sb, &key, root);
 	btrfs_put_root(root);
-	if (IS_ERR(inode)) {
-		err = PTR_ERR(inode);
-		goto fail;
-	}
-
-	srcu_read_unlock(&fs_info->subvol_srcu, index);
+	if (IS_ERR(inode))
+		return ERR_CAST(inode);
 
 	if (check_generation && generation != inode->i_generation) {
 		iput(inode);
@@ -102,9 +92,6 @@ static struct dentry *btrfs_get_dentry(struct super_block *sb, u64 objectid,
 	}
 
 	return d_obtain_alias(inode);
-fail:
-	srcu_read_unlock(&fs_info->subvol_srcu, index);
-	return ERR_PTR(err);
 }
 
 static struct dentry *btrfs_fh_to_parent(struct super_block *sb, struct fid *fh,
diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 8f44cbea6255..c6f9029e3d49 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -277,7 +277,6 @@ static int __btrfs_run_defrag_inode(struct btrfs_fs_info *fs_info,
 	struct btrfs_key key;
 	struct btrfs_ioctl_defrag_range_args range;
 	int num_defrag;
-	int index;
 	int ret;
 
 	/* get the inode */
@@ -285,8 +284,6 @@ static int __btrfs_run_defrag_inode(struct btrfs_fs_info *fs_info,
 	key.type = BTRFS_ROOT_ITEM_KEY;
 	key.offset = (u64)-1;
 
-	index = srcu_read_lock(&fs_info->subvol_srcu);
-
 	inode_root = btrfs_get_fs_root(fs_info, &key, true);
 	if (IS_ERR(inode_root)) {
 		ret = PTR_ERR(inode_root);
@@ -302,7 +299,6 @@ static int __btrfs_run_defrag_inode(struct btrfs_fs_info *fs_info,
 		ret = PTR_ERR(inode);
 		goto cleanup;
 	}
-	srcu_read_unlock(&fs_info->subvol_srcu, index);
 
 	/* do a chunk of defrag */
 	clear_bit(BTRFS_INODE_IN_DEFRAG, &BTRFS_I(inode)->runtime_flags);
@@ -338,7 +334,6 @@ static int __btrfs_run_defrag_inode(struct btrfs_fs_info *fs_info,
 	iput(inode);
 	return 0;
 cleanup:
-	srcu_read_unlock(&fs_info->subvol_srcu, index);
 	kmem_cache_free(btrfs_inode_defrag_cachep, defrag);
 	return ret;
 }
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index f7afa44d7cf3..10087e1a5946 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -5231,7 +5231,6 @@ struct inode *btrfs_lookup_dentry(struct inode *dir, struct dentry *dentry)
 	struct btrfs_root *sub_root = root;
 	struct btrfs_key location;
 	u8 di_type = 0;
-	int index;
 	int ret = 0;
 
 	if (dentry->d_name.len > BTRFS_NAME_LEN)
@@ -5258,7 +5257,6 @@ struct inode *btrfs_lookup_dentry(struct inode *dir, struct dentry *dentry)
 		return inode;
 	}
 
-	index = srcu_read_lock(&fs_info->subvol_srcu);
 	ret = fixup_tree_root_location(fs_info, dir, dentry,
 				       &location, &sub_root);
 	if (ret < 0) {
@@ -5271,7 +5269,6 @@ struct inode *btrfs_lookup_dentry(struct inode *dir, struct dentry *dentry)
 	}
 	if (root != sub_root)
 		btrfs_put_root(sub_root);
-	srcu_read_unlock(&fs_info->subvol_srcu, index);
 
 	if (!IS_ERR(inode) && root != sub_root) {
 		down_read(&fs_info->cleanup_work_sem);
diff --git a/fs/btrfs/send.c b/fs/btrfs/send.c
index 95aa0d54abec..717caf84a525 100644
--- a/fs/btrfs/send.c
+++ b/fs/btrfs/send.c
@@ -7065,7 +7065,6 @@ long btrfs_ioctl_send(struct file *mnt_file, struct btrfs_ioctl_send_args *arg)
 	int clone_sources_to_rollback = 0;
 	unsigned alloc_size;
 	int sort_clone_roots = 0;
-	int index;
 
 	if (!capable(CAP_SYS_ADMIN))
 		return -EPERM;
@@ -7192,11 +7191,8 @@ long btrfs_ioctl_send(struct file *mnt_file, struct btrfs_ioctl_send_args *arg)
 			key.type = BTRFS_ROOT_ITEM_KEY;
 			key.offset = (u64)-1;
 
-			index = srcu_read_lock(&fs_info->subvol_srcu);
-
 			clone_root = btrfs_get_fs_root(fs_info, &key, true);
 			if (IS_ERR(clone_root)) {
-				srcu_read_unlock(&fs_info->subvol_srcu, index);
 				ret = PTR_ERR(clone_root);
 				goto out;
 			}
@@ -7204,7 +7200,6 @@ long btrfs_ioctl_send(struct file *mnt_file, struct btrfs_ioctl_send_args *arg)
 			if (!btrfs_root_readonly(clone_root) ||
 			    btrfs_root_dead(clone_root)) {
 				spin_unlock(&clone_root->root_item_lock);
-				srcu_read_unlock(&fs_info->subvol_srcu, index);
 				btrfs_put_root(clone_root);
 				ret = -EPERM;
 				goto out;
@@ -7212,14 +7207,12 @@ long btrfs_ioctl_send(struct file *mnt_file, struct btrfs_ioctl_send_args *arg)
 			if (clone_root->dedupe_in_progress) {
 				dedupe_in_progress_warn(clone_root);
 				spin_unlock(&clone_root->root_item_lock);
-				srcu_read_unlock(&fs_info->subvol_srcu, index);
 				btrfs_put_root(clone_root);
 				ret = -EAGAIN;
 				goto out;
 			}
 			clone_root->send_in_progress++;
 			spin_unlock(&clone_root->root_item_lock);
-			srcu_read_unlock(&fs_info->subvol_srcu, index);
 
 			sctx->clone_roots[i].root = clone_root;
 			clone_sources_to_rollback = i + 1;
@@ -7233,11 +7226,8 @@ long btrfs_ioctl_send(struct file *mnt_file, struct btrfs_ioctl_send_args *arg)
 		key.type = BTRFS_ROOT_ITEM_KEY;
 		key.offset = (u64)-1;
 
-		index = srcu_read_lock(&fs_info->subvol_srcu);
-
 		sctx->parent_root = btrfs_get_fs_root(fs_info, &key, true);
 		if (IS_ERR(sctx->parent_root)) {
-			srcu_read_unlock(&fs_info->subvol_srcu, index);
 			ret = PTR_ERR(sctx->parent_root);
 			goto out;
 		}
@@ -7247,20 +7237,16 @@ long btrfs_ioctl_send(struct file *mnt_file, struct btrfs_ioctl_send_args *arg)
 		if (!btrfs_root_readonly(sctx->parent_root) ||
 				btrfs_root_dead(sctx->parent_root)) {
 			spin_unlock(&sctx->parent_root->root_item_lock);
-			srcu_read_unlock(&fs_info->subvol_srcu, index);
 			ret = -EPERM;
 			goto out;
 		}
 		if (sctx->parent_root->dedupe_in_progress) {
 			dedupe_in_progress_warn(sctx->parent_root);
 			spin_unlock(&sctx->parent_root->root_item_lock);
-			srcu_read_unlock(&fs_info->subvol_srcu, index);
 			ret = -EAGAIN;
 			goto out;
 		}
 		spin_unlock(&sctx->parent_root->root_item_lock);
-
-		srcu_read_unlock(&fs_info->subvol_srcu, index);
 	}
 
 	/*
diff --git a/fs/btrfs/tests/btrfs-tests.c b/fs/btrfs/tests/btrfs-tests.c
index 42e62fd2809c..999c14e5d0bd 100644
--- a/fs/btrfs/tests/btrfs-tests.c
+++ b/fs/btrfs/tests/btrfs-tests.c
@@ -134,14 +134,6 @@ struct btrfs_fs_info *btrfs_alloc_dummy_fs_info(u32 nodesize, u32 sectorsize)
 
 	fs_info->nodesize = nodesize;
 	fs_info->sectorsize = sectorsize;
-
-	if (init_srcu_struct(&fs_info->subvol_srcu)) {
-		kfree(fs_info->fs_devices);
-		kfree(fs_info->super_copy);
-		kfree(fs_info);
-		return NULL;
-	}
-
 	set_bit(BTRFS_FS_STATE_DUMMY_FS_INFO, &fs_info->fs_state);
 
 	test_mnt->mnt_sb->s_fs_info = fs_info;
@@ -191,7 +183,6 @@ void btrfs_free_dummy_fs_info(struct btrfs_fs_info *fs_info)
 	}
 	btrfs_free_qgroup_config(fs_info);
 	btrfs_free_fs_roots(fs_info);
-	cleanup_srcu_struct(&fs_info->subvol_srcu);
 	kfree(fs_info->super_copy);
 	btrfs_check_leaked_roots(fs_info);
 	btrfs_extent_buffer_leak_debug_check(fs_info);
-- 
2.24.1