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blk-mq: fix hang in bt_get()

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Avoid that if there are fewer hardware queues than CPU threads that
bt_get() can hang. The symptoms of the hang were as follows:

* All tags allocated for a particular hardware queue.
* (nr_tags) pending commands for that hardware queue.
* No pending commands for the software queues associated with that
  hardware queue.

Signed-off-by: Jens Axboe <axboe@fb.com>
This commit is contained in:
Bart Van Assche 2014-12-08 08:46:34 -07:00 • committed by Jens Axboe
commit b32232073e
1 changed files with 7 additions and 0 deletions
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7
block/blk-mq-tag.c
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@ -254,6 +254,13 @@ static int bt_get(struct blk_mq_alloc_data *data,
if (tag != -1)
break;
/*
* We're out of tags on this hardware queue, kick any
* pending IO submits before going to sleep waiting for
* some to complete.
*/
blk_mq_run_hw_queue(hctx, false);
blk_mq_put_ctx(data->ctx);
io_schedule();