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Subject[PATCH AUTOSEL 5.2 14/76] rq-qos: use a mb for got_token
Date
From: Josef Bacik <josef@toxicpanda.com>

[ Upstream commit ac38297f7038cd5b80d66f8809c7bbf5b70031f3 ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
block/blk-rq-qos.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/block/blk-rq-qos.c b/block/blk-rq-qos.c
index e3ab75e4df9ea..06d024204f504 100644
--- a/block/blk-rq-qos.c
+++ b/block/blk-rq-qos.c
@@ -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;
@@ -245,6 +246,7 @@ void rq_qos_wait(struct rq_wait *rqw, void *private_data,

prepare_to_wait_exclusive(&rqw->wait, &data.wq, TASK_UNINTERRUPTIBLE);
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)) {
@@ -255,6 +257,7 @@ 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;
--
2.20.1
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