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rq-qos: use a mb for got_token

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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: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Josef Bacik 2019-07-16 16:19:29 -04:00 committed by Jens Axboe
parent d14a9b389a
commit ac38297f70
1 changed files with 3 additions and 0 deletions
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3
block/blk-rq-qos.c
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@ -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;