From: Bart Van Assche <bvanassche@acm.org>
Date: Mon, 8 Dec 2014 15:46:34 +0000 (-0700)
Subject: blk-mq: fix hang in bt_get()
X-Git-Url: http://git.cdn.openwrt.org/?a=commitdiff_plain;h=b32232073e8061b41258bff2a10a06a91677480a;p=openwrt%2Fstaging%2Fblogic.git

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 230ef3056b72..eb55492e6875 100644
--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c
@@ -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();