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

f2fs: fix node_cnt race between extent node destroy and writeback

f2fs_destroy_extent_node() does not set FI_NO_EXTENT before clearing
extent nodes. When called from f2fs_drop_inode() with I_SYNC set,
concurrent kworker writeback can insert new extent nodes into the same
extent tree, racing with the destroy and triggering f2fs_bug_on() in
__destroy_extent_node(). The scenario is as follows:

drop inode                            writeback
 - iput
  - f2fs_drop_inode  // I_SYNC set
   - f2fs_destroy_extent_node
    - __destroy_extent_node
     - while (node_cnt) {
        write_lock(&et->lock)
        __free_extent_tree
        write_unlock(&et->lock)
                                       - __writeback_single_inode
                                        - f2fs_outplace_write_data
                                         - f2fs_update_read_extent_cache
                                          - __update_extent_tree_range
                                           // FI_NO_EXTENT not set,
                                           // insert new extent node
       } // node_cnt == 0, exit while
     - f2fs_bug_on(node_cnt)  // node_cnt > 0

Additionally, __update_extent_tree_range() only checks FI_NO_EXTENT for
EX_READ type, leaving EX_BLOCK_AGE updates completely unprotected.

This patch set FI_NO_EXTENT under et->lock in __destroy_extent_node(),
consistent with other callers (__update_extent_tree_range and
__drop_extent_tree) and check FI_NO_EXTENT for both EX_READ and
EX_BLOCK_AGE tree.