1 files changed, 88 insertions, 8 deletions

diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
index 6e556031a8f3..dcb510f38dda 100644
--- a/fs/btrfs/ctree.c
+++ b/fs/btrfs/ctree.c
@@ -114,6 +114,22 @@ noinline void btrfs_release_path(struct btrfs_path *p)
 }
 
 /*
+ * We want the transaction abort to print stack trace only for errors where the
+ * cause could be a bug, eg. due to ENOSPC, and not for common errors that are
+ * caused by external factors.
+ */
+bool __cold abort_should_print_stack(int errno)
+{
+	switch (errno) {
+	case -EIO:
+	case -EROFS:
+	case -ENOMEM:
+		return false;
+	}
+	return true;
+}
+
+/*
  * safely gets a reference on the root node of a tree.  A lock
  * is not taken, so a concurrent writer may put a different node
  * at the root of the tree.  See btrfs_lock_root_node for the
@@ -1447,6 +1463,11 @@ read_block_for_search(struct btrfs_root *root, struct btrfs_path *p,
 			return 0;
 		}
 
+		if (p->nowait) {
+			free_extent_buffer(tmp);
+			return -EAGAIN;
+		}
+
 		if (unlock_up)
 			btrfs_unlock_up_safe(p, level + 1);
 
@@ -1467,6 +1488,8 @@ read_block_for_search(struct btrfs_root *root, struct btrfs_path *p,
 			ret = -EAGAIN;
 
 		goto out;
+	} else if (p->nowait) {
+		return -EAGAIN;
 	}
 
 	if (unlock_up) {
@@ -1634,7 +1657,13 @@ static struct extent_buffer *btrfs_search_slot_get_root(struct btrfs_root *root,
 		 * We don't know the level of the root node until we actually
 		 * have it read locked
 		 */
-		b = btrfs_read_lock_root_node(root);
+		if (p->nowait) {
+			b = btrfs_try_read_lock_root_node(root);
+			if (IS_ERR(b))
+				return b;
+		} else {
+			b = btrfs_read_lock_root_node(root);
+		}
 		level = btrfs_header_level(b);
 		if (level > write_lock_level)
 			goto out;
@@ -1910,6 +1939,13 @@ int btrfs_search_slot(struct btrfs_trans_handle *trans, struct btrfs_root *root,
 	WARN_ON(p->nodes[0] != NULL);
 	BUG_ON(!cow && ins_len);
 
+	/*
+	 * For now only allow nowait for read only operations.  There's no
+	 * strict reason why we can't, we just only need it for reads so it's
+	 * only implemented for reads.
+	 */
+	ASSERT(!p->nowait || !cow);
+
 	if (ins_len < 0) {
 		lowest_unlock = 2;
 
@@ -1936,7 +1972,12 @@ int btrfs_search_slot(struct btrfs_trans_handle *trans, struct btrfs_root *root,
 
 	if (p->need_commit_sem) {
 		ASSERT(p->search_commit_root);
-		down_read(&fs_info->commit_root_sem);
+		if (p->nowait) {
+			if (!down_read_trylock(&fs_info->commit_root_sem))
+				return -EAGAIN;
+		} else {
+			down_read(&fs_info->commit_root_sem);
+		}
 	}
 
 again:
@@ -2075,11 +2116,22 @@ cow_done:
 
 		if (!p->skip_locking) {
 			level = btrfs_header_level(b);
+
+			btrfs_maybe_reset_lockdep_class(root, b);
+
 			if (level <= write_lock_level) {
 				btrfs_tree_lock(b);
 				p->locks[level] = BTRFS_WRITE_LOCK;
 			} else {
-				btrfs_tree_read_lock(b);
+				if (p->nowait) {
+					if (!btrfs_try_tree_read_lock(b)) {
+						free_extent_buffer(b);
+						ret = -EAGAIN;
+						goto done;
+					}
+				} else {
+					btrfs_tree_read_lock(b);
+				}
 				p->locks[level] = BTRFS_READ_LOCK;
 			}
 			p->nodes[level] = b;
@@ -2128,6 +2180,7 @@ int btrfs_search_old_slot(struct btrfs_root *root, const struct btrfs_key *key,
 
 	lowest_level = p->lowest_level;
 	WARN_ON(p->nodes[0] != NULL);
+	ASSERT(!p->nowait);
 
 	if (p->search_commit_root) {
 		BUG_ON(time_seq);
@@ -4429,6 +4482,7 @@ int btrfs_search_forward(struct btrfs_root *root, struct btrfs_key *min_key,
 	int ret = 1;
 	int keep_locks = path->keep_locks;
 
+	ASSERT(!path->nowait);
 	path->keep_locks = 1;
 again:
 	cur = btrfs_read_lock_root_node(root);
@@ -4609,6 +4663,13 @@ int btrfs_next_old_leaf(struct btrfs_root *root, struct btrfs_path *path,
 	int ret;
 	int i;
 
+	/*
+	 * The nowait semantics are used only for write paths, where we don't
+	 * use the tree mod log and sequence numbers.
+	 */
+	if (time_seq)
+		ASSERT(!path->nowait);
+
 	nritems = btrfs_header_nritems(path->nodes[0]);
 	if (nritems == 0)
 		return 1;
@@ -4627,7 +4688,14 @@ again:
 		if (path->need_commit_sem) {
 			path->need_commit_sem = 0;
 			need_commit_sem = true;
-			down_read(&fs_info->commit_root_sem);
+			if (path->nowait) {
+				if (!down_read_trylock(&fs_info->commit_root_sem)) {
+					ret = -EAGAIN;
+					goto done;
+				}
+			} else {
+				down_read(&fs_info->commit_root_sem);
+			}
 		}
 		ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
 	}
@@ -4703,7 +4771,7 @@ again:
 		next = c;
 		ret = read_block_for_search(root, path, &next, level,
 					    slot, &key);
-		if (ret == -EAGAIN)
+		if (ret == -EAGAIN && !path->nowait)
 			goto again;
 
 		if (ret < 0) {
@@ -4713,6 +4781,10 @@ again:
 
 		if (!path->skip_locking) {
 			ret = btrfs_try_tree_read_lock(next);
+			if (!ret && path->nowait) {
+				ret = -EAGAIN;
+				goto done;
+			}
 			if (!ret && time_seq) {
 				/*
 				 * If we don't get the lock, we may be racing
@@ -4743,7 +4815,7 @@ again:
 
 		ret = read_block_for_search(root, path, &next, level,
 					    0, &key);
-		if (ret == -EAGAIN)
+		if (ret == -EAGAIN && !path->nowait)
 			goto again;
 
 		if (ret < 0) {
@@ -4751,8 +4823,16 @@ again:
 			goto done;
 		}
 
-		if (!path->skip_locking)
-			btrfs_tree_read_lock(next);
+		if (!path->skip_locking) {
+			if (path->nowait) {
+				if (!btrfs_try_tree_read_lock(next)) {
+					ret = -EAGAIN;
+					goto done;
+				}
+			} else {
+				btrfs_tree_read_lock(next);
+			}
+		}
 	}
 	ret = 0;
 done: