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

jbd2: fix deadlock in jbd2_journal_cancel_revoke()

Commit f76d4c28a46a ("fs/jbd2: use sleeping version of
__find_get_block()") changed jbd2_journal_cancel_revoke() to use
__find_get_block_nonatomic() which holds the folio lock instead of
i_private_lock. This breaks the lock ordering (folio -> buffer) and
causes an ABBA deadlock when the filesystem blocksize < pagesize:

T1 T2
ext4_mkdir()
ext4_init_new_dir()
ext4_append()
ext4_getblk()
lock_buffer() <- A
sync_blockdev()
blkdev_writepages()
writeback_iter()
writeback_get_folio()
folio_lock() <- B
ext4_journal_get_create_access()
jbd2_journal_cancel_revoke()
__find_get_block_nonatomic()
folio_lock() <- B
block_write_full_folio()
lock_buffer() <- A

This can occasionally cause generic/013 to hang.

Fix by only calling __find_get_block_nonatomic() when the passed
buffer_head doesn't belong to the bdev, which is the only case that we
need to look up its bdev alias. Otherwise, the lookup is redundant since
the found buffer_head is equal to the one we passed in.