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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 <hch@infradead.org>
Cc: Ming Lei <tom.leiming@gmail.com>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Alexander Gordeev <agordeev@redhat.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
This commit is contained in:
Alexander Gordeev 2014-06-17 22:37:23 +02:00 committed by Jens Axboe
parent 2971c35f35
commit 86fb5c56cf
1 changed files with 6 additions and 9 deletions
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15
block/blk-mq-tag.c
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@ -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)
break;
if (was_empty)
atomic_set(&bs->wait_cnt, bt->wake_cnt);
blk_mq_put_ctx(data->ctx);
io_schedule();
@ -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++)
init_waitqueue_head(&bt->bs[i].wait);
bt_update_count(bt, depth);
for (i = 0; i < BT_WAIT_QUEUES; i++) {
init_waitqueue_head(&bt->bs[i].wait);
atomic_set(&bt->bs[i].wait_cnt, bt->wake_cnt);
}
return 0;
}