[PATCH v2] btrfs: add missing NULL check in btrfs_free_tree_block()

[Riyan Dhiman <riyandhiman14@gmail.com>]

In commit 3ba2d3648f9dc (btrfs: reflow btrfs_free_tree_block), the block
group lookup using btrfs_lookup_block_group() was added in btrfs_free_tree_block().
However, the return value of this function is not checked for a NULL result,
which can lead to null pointer dereferences if the block group is not found.

This patch adds a check to ensure that if btrfs_lookup_block_group() returns
NULL, the function will gracefully exit, preventing further operations that
rely on a valid block group pointer.

Signed-off-by: Riyan Dhiman <riyandhiman14@gmail.com>
---
v2: Added WARN_ON if block group is NULL instead of jump to out block.
v1: if block group is NULL, jump to out block.

Compile tested only

 fs/btrfs/extent-tree.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index a5966324607d..be031be3dfe5 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -3455,6 +3455,13 @@ int btrfs_free_tree_block(struct btrfs_trans_handle *trans,
 
 	bg = btrfs_lookup_block_group(fs_info, buf->start);
 
+	if (WARN_ON(!bg)) {
+	    btrfs_abort_transaction(trans, -ENOENT);
+	    btrfs_err(fs_info, "block group not found for extent buffer %llu generation %llu root %llu transaction %llu",
+				buf->start, btrfs_header_generation(buf), root_id,
+				trans->transid);
+	    return -ENOENT;
+	}
 	if (btrfs_header_flag(buf, BTRFS_HEADER_FLAG_WRITTEN)) {
 		pin_down_extent(trans, bg, buf->start, buf->len, 1);
 		btrfs_put_block_group(bg);
-- 
2.46.1