ext4: move percpu_rwsem protection into ext4_writepages()

ext4: move percpu_rwsem protection into ext4_writepages()

Move protection by percpu_rwsem from ext4_do_writepages() to
ext4_writepages(). We will not want to grab this protection during
transaction commits as that would be prone to deadlocks and the
protection is not needed. Move the shutdown state checking as well since
we want to be able to complete commit while the shutdown is in progress.

Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20221207112722.22220-7-jack@suse.cz
Signed-off-by: Theodore Ts'o <tytso@mit.edu>