vfs: partially sanitize i_state zeroing on inode creation

vfs: partially sanitize i_state zeroing on inode creation

new_inode used to have the following:
	spin_lock(&inode_lock);
	inodes_stat.nr_inodes++;
	list_add(&inode->i_list, &inode_in_use);
	list_add(&inode->i_sb_list, &sb->s_inodes);
	inode->i_ino = ++last_ino;
	inode->i_state = 0;
	spin_unlock(&inode_lock);

over time things disappeared, got moved around or got replaced (global
inode lock with a per-inode lock), eventually this got reduced to:
	spin_lock(&inode->i_lock);
	inode->i_state = 0;
	spin_unlock(&inode->i_lock);

But the lock acquire here does not synchronize against anyone.

Additionally iget5_locked performs i_state = 0 assignment without any
locks to begin with, the two combined look confusing at best.

It looks like the current state is a leftover which was not cleaned up.

Ideally it would be an invariant that i_state == 0 to begin with, but
achieving that would require dealing with all filesystem alloc handlers
one by one.

In the meantime drop the misleading locking and move i_state zeroing to
inode_init_always so that others don't need to deal with it by hand.

Signed-off-by: Mateusz Guzik <mjguzik@gmail.com>
Link: https://lore.kernel.org/r/20240611120626.513952-3-mjguzik@gmail.com
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>