block: internal dequeue shouldn't start timer

blkdev_dequeue_request() and elv_dequeue_request() are equivalent and
both start the timeout timer.  Barrier code dequeues the original
barrier request but doesn't passes the request itself to lower level
driver, only broken down proxy requests; however, as the original
barrier code goes through the same dequeue path and timeout timer is
started on it.  If barrier sequence takes long enough, this timer
expires but the low level driver has no idea about this request and
oops follows.

Timeout timer shouldn't have been started on the original barrier
request as it never goes through actual IO.  This patch unexports
elv_dequeue_request(), which has no external user anyway, and makes it
operate on elevator proper w/o adding the timer and make
blkdev_dequeue_request() call elv_dequeue_request() and add timer.
Internal users which don't pass the request to driver - barrier code
and end_that_request_last() - are converted to use
elv_dequeue_request().

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Mike Anderson <andmike@linux.vnet.ibm.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

1 files changed, 23 insertions, 1 deletions

diff --git a/block/blk-core.c b/block/blk-core.c
index 10e8a64a5a5b..7a779d7c69c9 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1637,6 +1637,28 @@ int blk_insert_cloned_request(struct request_queue *q, struct request *rq)
 EXPORT_SYMBOL_GPL(blk_insert_cloned_request);
 
 /**
+ * blkdev_dequeue_request - dequeue request and start timeout timer
+ * @req: request to dequeue
+ *
+ * Dequeue @req and start timeout timer on it.  This hands off the
+ * request to the driver.
+ *
+ * Block internal functions which don't want to start timer should
+ * call elv_dequeue_request().
+ */
+void blkdev_dequeue_request(struct request *req)
+{
+        elv_dequeue_request(req->q, req);
+
+        /*
+         * We are now handing the request to the hardware, add the
+         * timeout handler.
+         */
+        blk_add_timer(req);
+}
+EXPORT_SYMBOL(blkdev_dequeue_request);
+
+/**
  * __end_that_request_first - end I/O on a request
  * @req:      the request being processed
  * @error:    %0 for success, < %0 for error
@@ -1774,7 +1796,7 @@ static void end_that_request_last(struct request *req, int error)
                 blk_queue_end_tag(req->q, req);
 
         if (blk_queued_rq(req))
-                blkdev_dequeue_request(req);
+                elv_dequeue_request(req->q, req);
 
         if (unlikely(laptop_mode) && blk_fs_request(req))
                 laptop_io_completion();