In the Linux kernel, the following vulnerability has been resolved: btrfs: take commit root semaphore when iterating in mark_block_group_to

In the Linux kernel, the following vulnerability has been resolved:

btrfs: take commit root semaphore when iterating in mark_block_group_to_copy()

mark_block_group_to_copy() iterates over the commit root with
skip_locking=true. A concurrent transaction commit can swap and free
the commit root during iteration, causing use-after-free when
accessing extent buffers.

Fix it by using path->need_commit_sem to protect the commit root search.