block: kill swap_io_context()

It blindly copies everything in the io_context, including the lock.
That doesn't work so well for either lock ordering or lockdep.

There seems zero point in swapping io contexts on a request to request
merge, so the best point of action is to just remove it.
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

block/as-iosched.c

@@ -1268,22 +1268,8 @@ static void as_merged_requests(struct request_queue *q, struct request *req,
 	 */
 	if (!list_empty(&req->queuelist) && !list_empty(&next->queuelist)) {
 		if (time_before(rq_fifo_time(next), rq_fifo_time(req))) {
-			struct io_context *rioc = RQ_IOC(req);
-			struct io_context *nioc = RQ_IOC(next);
-
 			list_move(&req->queuelist, &next->queuelist);
 			rq_set_fifo_time(req, rq_fifo_time(next));
-			/*
-			 * Don't copy here but swap, because when anext is
-			 * removed below, it must contain the unused context
-			 */
-			if (rioc != nioc) {
-				double_spin_lock(&rioc->lock, &nioc->lock,
-								rioc < nioc);
-				swap_io_context(&rioc, &nioc);
-				double_spin_unlock(&rioc->lock, &nioc->lock,
-								rioc < nioc);
-			}
 		}
 	}
 

block/blk-ioc.c

@@ -176,15 +176,6 @@ void copy_io_context(struct io_context **pdst, struct io_context **psrc)
 }
 EXPORT_SYMBOL(copy_io_context);
 
-void swap_io_context(struct io_context **ioc1, struct io_context **ioc2)
-{
-	struct io_context *temp;
-	temp = *ioc1;
-	*ioc1 = *ioc2;
-	*ioc2 = temp;
-}
-EXPORT_SYMBOL(swap_io_context);
-
 int __init blk_ioc_init(void)
 {
 	iocontext_cachep = kmem_cache_create("blkdev_ioc",

include/linux/blkdev.h

@@ -39,7 +39,6 @@ void exit_io_context(void);
 struct io_context *get_io_context(gfp_t gfp_flags, int node);
 struct io_context *alloc_io_context(gfp_t gfp_flags, int node);
 void copy_io_context(struct io_context **pdst, struct io_context **psrc);
-void swap_io_context(struct io_context **ioc1, struct io_context **ioc2);
 
 struct request;
 typedef void (rq_end_io_fn)(struct request *, int);