ext4: remove bdev_try_to_free_page() callback

mainline inclusion
from mainline-5.14-rc1
commit 3b672e3a
category: bugfix
bugzilla: 50788
CVE: NA
---------------------------

After we introduce a jbd2 shrinker to release checkpointed buffer's
journal head, we could free buffer without bdev_try_to_free_page()
under memory pressure. So this patch remove the whole
bdev_try_to_free_page() callback directly. It also remove many
use-after-free issues relate to it together.

Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20210610112440.3438139-8-yi.zhang@huawei.com


Signed-off-by: Theodore Ts'o <tytso@mit.edu>

Conflict:
  fs/ext4/super.c
Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
Reviewed-by: Yang Erkun <yangerkun@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>