1 files changed, 55 insertions, 18 deletions

diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
index a4cb4b642987..617d4827eec2 100644
--- a/fs/btrfs/ctree.c
+++ b/fs/btrfs/ctree.c
@@ -367,7 +367,8 @@ int btrfs_copy_root(struct btrfs_trans_handle *trans,
 /*
  * check if the tree block can be shared by multiple trees
  */
-int btrfs_block_can_be_shared(struct btrfs_root *root,
+int btrfs_block_can_be_shared(struct btrfs_trans_handle *trans,
+			      struct btrfs_root *root,
 			      struct extent_buffer *buf)
 {
 	/*
@@ -376,11 +377,21 @@ int btrfs_block_can_be_shared(struct btrfs_root *root,
 	 * not allocated by tree relocation, we know the block is not shared.
 	 */
 	if (test_bit(BTRFS_ROOT_SHAREABLE, &root->state) &&
-	    buf != root->node && buf != root->commit_root &&
+	    buf != root->node &&
 	    (btrfs_header_generation(buf) <=
 	     btrfs_root_last_snapshot(&root->root_item) ||
-	     btrfs_header_flag(buf, BTRFS_HEADER_FLAG_RELOC)))
-		return 1;
+	     btrfs_header_flag(buf, BTRFS_HEADER_FLAG_RELOC))) {
+		if (buf != root->commit_root)
+			return 1;
+		/*
+		 * An extent buffer that used to be the commit root may still be
+		 * shared because the tree height may have increased and it
+		 * became a child of a higher level root. This can happen when
+		 * snapshotting a subvolume created in the current transaction.
+		 */
+		if (btrfs_header_generation(buf) == trans->transid)
+			return 1;
+	}
 
 	return 0;
 }
@@ -415,7 +426,7 @@ static noinline int update_ref_for_cow(struct btrfs_trans_handle *trans,
 	 * are only allowed for blocks use full backrefs.
 	 */
 
-	if (btrfs_block_can_be_shared(root, buf)) {
+	if (btrfs_block_can_be_shared(trans, root, buf)) {
 		ret = btrfs_lookup_extent_info(trans, fs_info, buf->start,
 					       btrfs_header_level(buf), 1,
 					       &refs, &flags);
@@ -682,18 +693,30 @@ noinline int btrfs_cow_block(struct btrfs_trans_handle *trans,
 	u64 search_start;
 	int ret;
 
-	if (test_bit(BTRFS_ROOT_DELETING, &root->state))
-		btrfs_err(fs_info,
-			"COW'ing blocks on a fs root that's being dropped");
-
-	if (trans->transaction != fs_info->running_transaction)
-		WARN(1, KERN_CRIT "trans %llu running %llu\n",
-		       trans->transid,
-		       fs_info->running_transaction->transid);
+	if (unlikely(test_bit(BTRFS_ROOT_DELETING, &root->state))) {
+		btrfs_abort_transaction(trans, -EUCLEAN);
+		btrfs_crit(fs_info,
+		   "attempt to COW block %llu on root %llu that is being deleted",
+			   buf->start, btrfs_root_id(root));
+		return -EUCLEAN;
+	}
 
-	if (trans->transid != fs_info->generation)
-		WARN(1, KERN_CRIT "trans %llu running %llu\n",
-		       trans->transid, fs_info->generation);
+	/*
+	 * COWing must happen through a running transaction, which always
+	 * matches the current fs generation (it's a transaction with a state
+	 * less than TRANS_STATE_UNBLOCKED). If it doesn't, then turn the fs
+	 * into error state to prevent the commit of any transaction.
+	 */
+	if (unlikely(trans->transaction != fs_info->running_transaction ||
+		     trans->transid != fs_info->generation)) {
+		btrfs_abort_transaction(trans, -EUCLEAN);
+		btrfs_crit(fs_info,
+"unexpected transaction when attempting to COW block %llu on root %llu, transaction %llu running transaction %llu fs generation %llu",
+			   buf->start, btrfs_root_id(root), trans->transid,
+			   fs_info->running_transaction->transid,
+			   fs_info->generation);
+		return -EUCLEAN;
+	}
 
 	if (!should_cow_block(trans, root, buf)) {
 		*cow_ret = buf;
@@ -805,8 +828,22 @@ int btrfs_realloc_node(struct btrfs_trans_handle *trans,
 	int progress_passed = 0;
 	struct btrfs_disk_key disk_key;
 
-	WARN_ON(trans->transaction != fs_info->running_transaction);
-	WARN_ON(trans->transid != fs_info->generation);
+	/*
+	 * COWing must happen through a running transaction, which always
+	 * matches the current fs generation (it's a transaction with a state
+	 * less than TRANS_STATE_UNBLOCKED). If it doesn't, then turn the fs
+	 * into error state to prevent the commit of any transaction.
+	 */
+	if (unlikely(trans->transaction != fs_info->running_transaction ||
+		     trans->transid != fs_info->generation)) {
+		btrfs_abort_transaction(trans, -EUCLEAN);
+		btrfs_crit(fs_info,
+"unexpected transaction when attempting to reallocate parent %llu for root %llu, transaction %llu running transaction %llu fs generation %llu",
+			   parent->start, btrfs_root_id(root), trans->transid,
+			   fs_info->running_transaction->transid,
+			   fs_info->generation);
+		return -EUCLEAN;
+	}
 
 	parent_nritems = btrfs_header_nritems(parent);
 	blocksize = fs_info->nodesize;