blk-mq: fix potential io hang by wrong 'wake_batch'

In __blk_mq_tag_busy/idle(), updating 'active_queues' and calculating
'wake_batch' is not atomic:

t1:			t2:
_blk_mq_tag_busy	blk_mq_tag_busy
inc active_queues
// assume 1->2
			inc active_queues
			// 2 -> 3
			blk_mq_update_wake_batch
			// calculate based on 3
blk_mq_update_wake_batch
/* calculate based on 2, while active_queues is actually 3. */

Fix this problem by protecting them wih 'tags->lock', this is not a hot
path, so performance should not be concerned. And now that all writers
are inside the lock, switch 'actives_queues' from atomic to unsigned
int.

Fixes: 180dccb0 ("blk-mq: fix tag_get wait task can't be awakened")
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20230610023043.2559121-1-yukuai1@huaweicloud.com


Signed-off-by: Jens Axboe <axboe@kernel.dk>