blk-mq: fix hang in bt_get()
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>
diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
index 230ef30..eb55492 100644
--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c
@@ -254,6 +254,13 @@
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();