Commit 255bb490 authored Mar 02, 2011 by Tejun Heo Committed by Jens Axboe Mar 02, 2011

block: blk-flush shouldn't call directly into q->request_fn() __blk_run_queue()

blk-flush decomposes a flush into sequence of multiple requests.  On
completion of a request, the next one is queued; however, block layer
must not implicitly call into q->request_fn() directly from completion
path.  This makes the queue behave unexpectedly when seen from the
drivers and violates the assumption that q->request_fn() is called
with process context + queue_lock.

This patch makes blk-flush the following two changes to make sure
q->request_fn() is not called directly from request completion path.

- blk_flush_complete_seq_end_io() now asks __blk_run_queue() to always
  use kblockd instead of calling directly into q->request_fn().

- queue_next_fseq() uses ELEVATOR_INSERT_REQUEUE instead of
  ELEVATOR_INSERT_FRONT so that elv_insert() doesn't try to unplug the
  request queue directly.

Reported by Jan in the following threads.

 http://thread.gmane.org/gmane.linux.ide/48778
 http://thread.gmane.org/gmane.linux.ide/48786



stable: applicable to v2.6.37.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Jan Beulich <JBeulich@novell.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: stable@kernel.org
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

parent 1654e741

block/blk-flush.c

+5 −3

Original line number	Original line	Diff line number	Diff line
	@@ -66,10 +66,12 @@ static void blk_flush_complete_seq_end_io(struct request_queue *q,

	/*		/*
	* Moving a request silently to empty queue_head may stall the		* Moving a request silently to empty queue_head may stall the
	* queue. Kick the queue in those cases.		* queue. Kick the queue in those cases. This function is called
			* from request completion path and calling directly into
			* request_fn may confuse the driver. Always use kblockd.
	*/		*/
	if (was_empty && next_rq)		if (was_empty && next_rq)
	__blk_run_queue(q, false);		__blk_run_queue(q, true);
	}		}

	static void pre_flush_end_io(struct request *rq, int error)		static void pre_flush_end_io(struct request *rq, int error)
	@@ -130,7 +132,7 @@ static struct request queue_next_fseq(struct request_queue q)
	BUG();		BUG();
	}		}

	elv_insert(q, rq, ELEVATOR_INSERT_FRONT);		elv_insert(q, rq, ELEVATOR_INSERT_REQUEUE);
	return rq;		return rq;
	}		}