1 files changed, 308 insertions, 49 deletions

diff --git a/fs/btrfs/send.c b/fs/btrfs/send.c
index 6bdcb9d481d5..d8ccb62aa7d2 100644
--- a/fs/btrfs/send.c
+++ b/fs/btrfs/send.c
@@ -24,6 +24,7 @@
 #include "transaction.h"
 #include "compression.h"
 #include "xattr.h"
+#include "print-tree.h"
 
 /*
  * Maximum number of references an extent can have in order for us to attempt to
@@ -98,6 +99,15 @@ struct send_ctx {
 	struct btrfs_key *cmp_key;
 
 	/*
+	 * Keep track of the generation of the last transaction that was used
+	 * for relocating a block group. This is periodically checked in order
+	 * to detect if a relocation happened since the last check, so that we
+	 * don't operate on stale extent buffers for nodes (level >= 1) or on
+	 * stale disk_bytenr values of file extent items.
+	 */
+	u64 last_reloc_trans;
+
+	/*
 	 * infos of the currently processed inode. In case of deleted inodes,
 	 * these are the values from the deleted inode.
 	 */
@@ -1421,6 +1431,26 @@ static int find_extent_clone(struct send_ctx *sctx,
 	if (ret < 0)
 		goto out;
 
+	down_read(&fs_info->commit_root_sem);
+	if (fs_info->last_reloc_trans > sctx->last_reloc_trans) {
+		/*
+		 * A transaction commit for a transaction in which block group
+		 * relocation was done just happened.
+		 * The disk_bytenr of the file extent item we processed is
+		 * possibly stale, referring to the extent's location before
+		 * relocation. So act as if we haven't found any clone sources
+		 * and fallback to write commands, which will read the correct
+		 * data from the new extent location. Otherwise we will fail
+		 * below because we haven't found our own back reference or we
+		 * could be getting incorrect sources in case the old extent
+		 * was already reallocated after the relocation.
+		 */
+		up_read(&fs_info->commit_root_sem);
+		ret = -ENOENT;
+		goto out;
+	}
+	up_read(&fs_info->commit_root_sem);
+
 	if (!backref_ctx.found_itself) {
 		/* found a bug in backref code? */
 		ret = -EIO;
@@ -6583,6 +6613,50 @@ static int changed_cb(struct btrfs_path *left_path,
 {
 	int ret = 0;
 
+	/*
+	 * We can not hold the commit root semaphore here. This is because in
+	 * the case of sending and receiving to the same filesystem, using a
+	 * pipe, could result in a deadlock:
+	 *
+	 * 1) The task running send blocks on the pipe because it's full;
+	 *
+	 * 2) The task running receive, which is the only consumer of the pipe,
+	 *    is waiting for a transaction commit (for example due to a space
+	 *    reservation when doing a write or triggering a transaction commit
+	 *    when creating a subvolume);
+	 *
+	 * 3) The transaction is waiting to write lock the commit root semaphore,
+	 *    but can not acquire it since it's being held at 1).
+	 *
+	 * Down this call chain we write to the pipe through kernel_write().
+	 * The same type of problem can also happen when sending to a file that
+	 * is stored in the same filesystem - when reserving space for a write
+	 * into the file, we can trigger a transaction commit.
+	 *
+	 * Our caller has supplied us with clones of leaves from the send and
+	 * parent roots, so we're safe here from a concurrent relocation and
+	 * further reallocation of metadata extents while we are here. Below we
+	 * also assert that the leaves are clones.
+	 */
+	lockdep_assert_not_held(&sctx->send_root->fs_info->commit_root_sem);
+
+	/*
+	 * We always have a send root, so left_path is never NULL. We will not
+	 * have a leaf when we have reached the end of the send root but have
+	 * not yet reached the end of the parent root.
+	 */
+	if (left_path->nodes[0])
+		ASSERT(test_bit(EXTENT_BUFFER_UNMAPPED,
+				&left_path->nodes[0]->bflags));
+	/*
+	 * When doing a full send we don't have a parent root, so right_path is
+	 * NULL. When doing an incremental send, we may have reached the end of
+	 * the parent root already, so we don't have a leaf at right_path.
+	 */
+	if (right_path && right_path->nodes[0])
+		ASSERT(test_bit(EXTENT_BUFFER_UNMAPPED,
+				&right_path->nodes[0]->bflags));
+
 	if (result == BTRFS_COMPARE_TREE_SAME) {
 		if (key->type == BTRFS_INODE_REF_KEY ||
 		    key->type == BTRFS_INODE_EXTREF_KEY) {
@@ -6629,14 +6703,46 @@ out:
 	return ret;
 }
 
+static int search_key_again(const struct send_ctx *sctx,
+			    struct btrfs_root *root,
+			    struct btrfs_path *path,
+			    const struct btrfs_key *key)
+{
+	int ret;
+
+	if (!path->need_commit_sem)
+		lockdep_assert_held_read(&root->fs_info->commit_root_sem);
+
+	/*
+	 * Roots used for send operations are readonly and no one can add,
+	 * update or remove keys from them, so we should be able to find our
+	 * key again. The only exception is deduplication, which can operate on
+	 * readonly roots and add, update or remove keys to/from them - but at
+	 * the moment we don't allow it to run in parallel with send.
+	 */
+	ret = btrfs_search_slot(NULL, root, key, path, 0, 0);
+	ASSERT(ret <= 0);
+	if (ret > 0) {
+		btrfs_print_tree(path->nodes[path->lowest_level], false);
+		btrfs_err(root->fs_info,
+"send: key (%llu %u %llu) not found in %s root %llu, lowest_level %d, slot %d",
+			  key->objectid, key->type, key->offset,
+			  (root == sctx->parent_root ? "parent" : "send"),
+			  root->root_key.objectid, path->lowest_level,
+			  path->slots[path->lowest_level]);
+		return -EUCLEAN;
+	}
+
+	return ret;
+}
+
 static int full_send_tree(struct send_ctx *sctx)
 {
 	int ret;
 	struct btrfs_root *send_root = sctx->send_root;
 	struct btrfs_key key;
+	struct btrfs_fs_info *fs_info = send_root->fs_info;
 	struct btrfs_path *path;
-	struct extent_buffer *eb;
-	int slot;
 
 	path = alloc_path_for_send();
 	if (!path)
@@ -6647,6 +6753,10 @@ static int full_send_tree(struct send_ctx *sctx)
 	key.type = BTRFS_INODE_ITEM_KEY;
 	key.offset = 0;
 
+	down_read(&fs_info->commit_root_sem);
+	sctx->last_reloc_trans = fs_info->last_reloc_trans;
+	up_read(&fs_info->commit_root_sem);
+
 	ret = btrfs_search_slot_for_read(send_root, &key, path, 1, 0);
 	if (ret < 0)
 		goto out;
@@ -6654,15 +6764,35 @@ static int full_send_tree(struct send_ctx *sctx)
 		goto out_finish;
 
 	while (1) {
-		eb = path->nodes[0];
-		slot = path->slots[0];
-		btrfs_item_key_to_cpu(eb, &key, slot);
+		btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0]);
 
 		ret = changed_cb(path, NULL, &key,
 				 BTRFS_COMPARE_TREE_NEW, sctx);
 		if (ret < 0)
 			goto out;
 
+		down_read(&fs_info->commit_root_sem);
+		if (fs_info->last_reloc_trans > sctx->last_reloc_trans) {
+			sctx->last_reloc_trans = fs_info->last_reloc_trans;
+			up_read(&fs_info->commit_root_sem);
+			/*
+			 * A transaction used for relocating a block group was
+			 * committed or is about to finish its commit. Release
+			 * our path (leaf) and restart the search, so that we
+			 * avoid operating on any file extent items that are
+			 * stale, with a disk_bytenr that reflects a pre
+			 * relocation value. This way we avoid as much as
+			 * possible to fallback to regular writes when checking
+			 * if we can clone file ranges.
+			 */
+			btrfs_release_path(path);
+			ret = search_key_again(sctx, send_root, path, &key);
+			if (ret < 0)
+				goto out;
+		} else {
+			up_read(&fs_info->commit_root_sem);
+		}
+
 		ret = btrfs_next_item(send_root, path);
 		if (ret < 0)
 			goto out;
@@ -6680,6 +6810,20 @@ out:
 	return ret;
 }
 
+static int replace_node_with_clone(struct btrfs_path *path, int level)
+{
+	struct extent_buffer *clone;
+
+	clone = btrfs_clone_extent_buffer(path->nodes[level]);
+	if (!clone)
+		return -ENOMEM;
+
+	free_extent_buffer(path->nodes[level]);
+	path->nodes[level] = clone;
+
+	return 0;
+}
+
 static int tree_move_down(struct btrfs_path *path, int *level, u64 reada_min_gen)
 {
 	struct extent_buffer *eb;
@@ -6689,6 +6833,8 @@ static int tree_move_down(struct btrfs_path *path, int *level, u64 reada_min_gen
 	u64 reada_max;
 	u64 reada_done = 0;
 
+	lockdep_assert_held_read(&parent->fs_info->commit_root_sem);
+
 	BUG_ON(*level == 0);
 	eb = btrfs_read_node_slot(parent, slot);
 	if (IS_ERR(eb))
@@ -6712,6 +6858,10 @@ static int tree_move_down(struct btrfs_path *path, int *level, u64 reada_min_gen
 	path->nodes[*level - 1] = eb;
 	path->slots[*level - 1] = 0;
 	(*level)--;
+
+	if (*level == 0)
+		return replace_node_with_clone(path, 0);
+
 	return 0;
 }
 
@@ -6725,8 +6875,10 @@ static int tree_move_next_or_upnext(struct btrfs_path *path,
 	path->slots[*level]++;
 
 	while (path->slots[*level] >= nritems) {
-		if (*level == root_level)
+		if (*level == root_level) {
+			path->slots[*level] = nritems - 1;
 			return -1;
+		}
 
 		/* move upnext */
 		path->slots[*level] = 0;
@@ -6758,14 +6910,20 @@ static int tree_advance(struct btrfs_path *path,
 	} else {
 		ret = tree_move_down(path, level, reada_min_gen);
 	}
-	if (ret >= 0) {
-		if (*level == 0)
-			btrfs_item_key_to_cpu(path->nodes[*level], key,
-					path->slots[*level]);
-		else
-			btrfs_node_key_to_cpu(path->nodes[*level], key,
-					path->slots[*level]);
-	}
+
+	/*
+	 * Even if we have reached the end of a tree, ret is -1, update the key
+	 * anyway, so that in case we need to restart due to a block group
+	 * relocation, we can assert that the last key of the root node still
+	 * exists in the tree.
+	 */
+	if (*level == 0)
+		btrfs_item_key_to_cpu(path->nodes[*level], key,
+				      path->slots[*level]);
+	else
+		btrfs_node_key_to_cpu(path->nodes[*level], key,
+				      path->slots[*level]);
+
 	return ret;
 }
 
@@ -6795,6 +6953,97 @@ static int tree_compare_item(struct btrfs_path *left_path,
 }
 
 /*
+ * A transaction used for relocating a block group was committed or is about to
+ * finish its commit. Release our paths and restart the search, so that we are
+ * not using stale extent buffers:
+ *
+ * 1) For levels > 0, we are only holding references of extent buffers, without
+ *    any locks on them, which does not prevent them from having been relocated
+ *    and reallocated after the last time we released the commit root semaphore.
+ *    The exception are the root nodes, for which we always have a clone, see
+ *    the comment at btrfs_compare_trees();
+ *
+ * 2) For leaves, level 0, we are holding copies (clones) of extent buffers, so
+ *    we are safe from the concurrent relocation and reallocation. However they
+ *    can have file extent items with a pre relocation disk_bytenr value, so we
+ *    restart the start from the current commit roots and clone the new leaves so
+ *    that we get the post relocation disk_bytenr values. Not doing so, could
+ *    make us clone the wrong data in case there are new extents using the old
+ *    disk_bytenr that happen to be shared.
+ */
+static int restart_after_relocation(struct btrfs_path *left_path,
+				    struct btrfs_path *right_path,
+				    const struct btrfs_key *left_key,
+				    const struct btrfs_key *right_key,
+				    int left_level,
+				    int right_level,
+				    const struct send_ctx *sctx)
+{
+	int root_level;
+	int ret;
+
+	lockdep_assert_held_read(&sctx->send_root->fs_info->commit_root_sem);
+
+	btrfs_release_path(left_path);
+	btrfs_release_path(right_path);
+
+	/*
+	 * Since keys can not be added or removed to/from our roots because they
+	 * are readonly and we do not allow deduplication to run in parallel
+	 * (which can add, remove or change keys), the layout of the trees should
+	 * not change.
+	 */
+	left_path->lowest_level = left_level;
+	ret = search_key_again(sctx, sctx->send_root, left_path, left_key);
+	if (ret < 0)
+		return ret;
+
+	right_path->lowest_level = right_level;
+	ret = search_key_again(sctx, sctx->parent_root, right_path, right_key);
+	if (ret < 0)
+		return ret;
+
+	/*
+	 * If the lowest level nodes are leaves, clone them so that they can be
+	 * safely used by changed_cb() while not under the protection of the
+	 * commit root semaphore, even if relocation and reallocation happens in
+	 * parallel.
+	 */
+	if (left_level == 0) {
+		ret = replace_node_with_clone(left_path, 0);
+		if (ret < 0)
+			return ret;
+	}
+
+	if (right_level == 0) {
+		ret = replace_node_with_clone(right_path, 0);
+		if (ret < 0)
+			return ret;
+	}
+
+	/*
+	 * Now clone the root nodes (unless they happen to be the leaves we have
+	 * already cloned). This is to protect against concurrent snapshotting of
+	 * the send and parent roots (see the comment at btrfs_compare_trees()).
+	 */
+	root_level = btrfs_header_level(sctx->send_root->commit_root);
+	if (root_level > 0) {
+		ret = replace_node_with_clone(left_path, root_level);
+		if (ret < 0)
+			return ret;
+	}
+
+	root_level = btrfs_header_level(sctx->parent_root->commit_root);
+	if (root_level > 0) {
+		ret = replace_node_with_clone(right_path, root_level);
+		if (ret < 0)
+			return ret;
+	}
+
+	return 0;
+}
+
+/*
  * This function compares two trees and calls the provided callback for
  * every changed/new/deleted item it finds.
  * If shared tree blocks are encountered, whole subtrees are skipped, making
@@ -6822,10 +7071,10 @@ static int btrfs_compare_trees(struct btrfs_root *left_root,
 	int right_root_level;
 	int left_level;
 	int right_level;
-	int left_end_reached;
-	int right_end_reached;
-	int advance_left;
-	int advance_right;
+	int left_end_reached = 0;
+	int right_end_reached = 0;
+	int advance_left = 0;
+	int advance_right = 0;
 	u64 left_blockptr;
 	u64 right_blockptr;
 	u64 left_gen;
@@ -6893,12 +7142,18 @@ static int btrfs_compare_trees(struct btrfs_root *left_root,
 	down_read(&fs_info->commit_root_sem);
 	left_level = btrfs_header_level(left_root->commit_root);
 	left_root_level = left_level;
+	/*
+	 * We clone the root node of the send and parent roots to prevent races
+	 * with snapshot creation of these roots. Snapshot creation COWs the
+	 * root node of a tree, so after the transaction is committed the old
+	 * extent can be reallocated while this send operation is still ongoing.
+	 * So we clone them, under the commit root semaphore, to be race free.
+	 */
 	left_path->nodes[left_level] =
 			btrfs_clone_extent_buffer(left_root->commit_root);
 	if (!left_path->nodes[left_level]) {
-		up_read(&fs_info->commit_root_sem);
 		ret = -ENOMEM;
-		goto out;
+		goto out_unlock;
 	}
 
 	right_level = btrfs_header_level(right_root->commit_root);
@@ -6906,9 +7161,8 @@ static int btrfs_compare_trees(struct btrfs_root *left_root,
 	right_path->nodes[right_level] =
 			btrfs_clone_extent_buffer(right_root->commit_root);
 	if (!right_path->nodes[right_level]) {
-		up_read(&fs_info->commit_root_sem);
 		ret = -ENOMEM;
-		goto out;
+		goto out_unlock;
 	}
 	/*
 	 * Our right root is the parent root, while the left root is the "send"
@@ -6918,7 +7172,6 @@ static int btrfs_compare_trees(struct btrfs_root *left_root,
 	 * will need to read them at some point.
 	 */
 	reada_min_gen = btrfs_header_generation(right_root->commit_root);
-	up_read(&fs_info->commit_root_sem);
 
 	if (left_level == 0)
 		btrfs_item_key_to_cpu(left_path->nodes[left_level],
@@ -6933,11 +7186,26 @@ static int btrfs_compare_trees(struct btrfs_root *left_root,
 		btrfs_node_key_to_cpu(right_path->nodes[right_level],
 				&right_key, right_path->slots[right_level]);
 
-	left_end_reached = right_end_reached = 0;
-	advance_left = advance_right = 0;
+	sctx->last_reloc_trans = fs_info->last_reloc_trans;
 
 	while (1) {
-		cond_resched();
+		if (need_resched() ||
+		    rwsem_is_contended(&fs_info->commit_root_sem)) {
+			up_read(&fs_info->commit_root_sem);
+			cond_resched();
+			down_read(&fs_info->commit_root_sem);
+		}
+
+		if (fs_info->last_reloc_trans > sctx->last_reloc_trans) {
+			ret = restart_after_relocation(left_path, right_path,
+						       &left_key, &right_key,
+						       left_level, right_level,
+						       sctx);
+			if (ret < 0)
+				goto out_unlock;
+			sctx->last_reloc_trans = fs_info->last_reloc_trans;
+		}
+
 		if (advance_left && !left_end_reached) {
 			ret = tree_advance(left_path, &left_level,
 					left_root_level,
@@ -6946,7 +7214,7 @@ static int btrfs_compare_trees(struct btrfs_root *left_root,
 			if (ret == -1)
 				left_end_reached = ADVANCE;
 			else if (ret < 0)
-				goto out;
+				goto out_unlock;
 			advance_left = 0;
 		}
 		if (advance_right && !right_end_reached) {
@@ -6957,54 +7225,55 @@ static int btrfs_compare_trees(struct btrfs_root *left_root,
 			if (ret == -1)
 				right_end_reached = ADVANCE;
 			else if (ret < 0)
-				goto out;
+				goto out_unlock;
 			advance_right = 0;
 		}
 
 		if (left_end_reached && right_end_reached) {
 			ret = 0;
-			goto out;
+			goto out_unlock;
 		} else if (left_end_reached) {
 			if (right_level == 0) {
+				up_read(&fs_info->commit_root_sem);
 				ret = changed_cb(left_path, right_path,
 						&right_key,
 						BTRFS_COMPARE_TREE_DELETED,
 						sctx);
 				if (ret < 0)
 					goto out;
+				down_read(&fs_info->commit_root_sem);
 			}
 			advance_right = ADVANCE;
 			continue;
 		} else if (right_end_reached) {
 			if (left_level == 0) {
+				up_read(&fs_info->commit_root_sem);
 				ret = changed_cb(left_path, right_path,
 						&left_key,
 						BTRFS_COMPARE_TREE_NEW,
 						sctx);
 				if (ret < 0)
 					goto out;
+				down_read(&fs_info->commit_root_sem);
 			}
 			advance_left = ADVANCE;
 			continue;
 		}
 
 		if (left_level == 0 && right_level == 0) {
+			up_read(&fs_info->commit_root_sem);
 			cmp = btrfs_comp_cpu_keys(&left_key, &right_key);
 			if (cmp < 0) {
 				ret = changed_cb(left_path, right_path,
 						&left_key,
 						BTRFS_COMPARE_TREE_NEW,
 						sctx);
-				if (ret < 0)
-					goto out;
 				advance_left = ADVANCE;
 			} else if (cmp > 0) {
 				ret = changed_cb(left_path, right_path,
 						&right_key,
 						BTRFS_COMPARE_TREE_DELETED,
 						sctx);
-				if (ret < 0)
-					goto out;
 				advance_right = ADVANCE;
 			} else {
 				enum btrfs_compare_tree_result result;
@@ -7018,11 +7287,13 @@ static int btrfs_compare_trees(struct btrfs_root *left_root,
 					result = BTRFS_COMPARE_TREE_SAME;
 				ret = changed_cb(left_path, right_path,
 						 &left_key, result, sctx);
-				if (ret < 0)
-					goto out;
 				advance_left = ADVANCE;
 				advance_right = ADVANCE;
 			}
+
+			if (ret < 0)
+				goto out;
+			down_read(&fs_info->commit_root_sem);
 		} else if (left_level == right_level) {
 			cmp = btrfs_comp_cpu_keys(&left_key, &right_key);
 			if (cmp < 0) {
@@ -7062,6 +7333,8 @@ static int btrfs_compare_trees(struct btrfs_root *left_root,
 		}
 	}
 
+out_unlock:
+	up_read(&fs_info->commit_root_sem);
 out:
 	btrfs_free_path(left_path);
 	btrfs_free_path(right_path);
@@ -7411,21 +7684,7 @@ long btrfs_ioctl_send(struct file *mnt_file, struct btrfs_ioctl_send_args *arg)
 	if (ret)
 		goto out;
 
-	spin_lock(&fs_info->send_reloc_lock);
-	if (test_bit(BTRFS_FS_RELOC_RUNNING, &fs_info->flags)) {
-		spin_unlock(&fs_info->send_reloc_lock);
-		btrfs_warn_rl(fs_info,
-		"cannot run send because a relocation operation is in progress");
-		ret = -EAGAIN;
-		goto out;
-	}
-	fs_info->send_in_progress++;
-	spin_unlock(&fs_info->send_reloc_lock);
-
 	ret = send_subvol(sctx);
-	spin_lock(&fs_info->send_reloc_lock);
-	fs_info->send_in_progress--;
-	spin_unlock(&fs_info->send_reloc_lock);
 	if (ret < 0)
 		goto out;