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Commit ac38297f authored by Josef Bacik's avatar Josef Bacik Committed by Jens Axboe
Browse files

rq-qos: use a mb for got_token 



Oleg noticed that our checking of data.got_token is unsafe in the
cleanup case, and should really use a memory barrier.  Use a wmb on the
write side, and a rmb() on the read side.  We don't need one in the main
loop since we're saved by set_current_state().

Reviewed-by: default avatarOleg Nesterov <oleg@redhat.com>
Signed-off-by: default avatarJosef Bacik <josef@toxicpanda.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent d14a9b38

block/blk-rq-qos.c

+3 −0
Original line number Diff line number Diff line
@@ -202,6 +202,7 @@ static int rq_qos_wake_function(struct wait_queue_entry *curr, 
		return -1;



	data->got_token = true;

	smp_wmb();

	list_del_init(&curr->entry);

	wake_up_process(data->task);

	return 1;
@@ -246,6 +247,7 @@ void rq_qos_wait(struct rq_wait *rqw, void *private_data, 
	prepare_to_wait_exclusive(&rqw->wait, &data.wq, TASK_UNINTERRUPTIBLE);

	has_sleeper = !wq_has_single_sleeper(&rqw->wait);

	do {

		/* The memory barrier in set_task_state saves us here. */

		if (data.got_token)

			break;

		if (!has_sleeper && acquire_inflight_cb(rqw, private_data)) {
@@ -256,6 +258,7 @@ void rq_qos_wait(struct rq_wait *rqw, void *private_data, 
			 * which means we now have two. Put our local token

			 * and wake anyone else potentially waiting for one.

			 */

			smp_rmb();

			if (data.got_token)

				cleanup_cb(rqw, private_data);

			break;