Commit 86fb5c56 authored by Alexander Gordeev's avatar Alexander Gordeev Committed by Jens Axboe
Browse files

blk-mq: bitmap tag: fix races in bt_get() function

This update fixes few issues in bt_get() function:

- list_empty(&wait.task_list) check is not protected;

- was_empty check is always true which results in *every* thread
  entering the loop resets bt_wait_state::wait_cnt counter rather
  than every bt->wake_cnt'th thread;

- 'bt_wait_state::wait_cnt' counter update is redundant, since
  it also gets reset in bt_clear_tag() function;

Cc: Christoph Hellwig <>
Cc: Ming Lei <>
Cc: Jens Axboe <>
Signed-off-by: default avatarAlexander Gordeev <>
Signed-off-by: default avatarJens Axboe <>
parent 2971c35f
......@@ -248,18 +248,12 @@ static int bt_get(struct blk_mq_alloc_data *data,
bs = bt_wait_ptr(bt, hctx);
do {
bool was_empty;
was_empty = list_empty(&wait.task_list);
prepare_to_wait(&bs->wait, &wait, TASK_UNINTERRUPTIBLE);
tag = __bt_get(hctx, bt, last_tag);
if (tag != -1)
if (was_empty)
atomic_set(&bs->wait_cnt, bt->wake_cnt);
......@@ -519,10 +513,13 @@ static int bt_alloc(struct blk_mq_bitmap_tags *bt, unsigned int depth,
return -ENOMEM;
for (i = 0; i < BT_WAIT_QUEUES; i++)
bt_update_count(bt, depth);
for (i = 0; i < BT_WAIT_QUEUES; i++) {
atomic_set(&bt->bs[i].wait_cnt, bt->wake_cnt);
bt_update_count(bt, depth);
return 0;
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