[PATCH] blk: clear completion stack pointer on return

From: Jens Axboe <axboe@suse.de>

It doesn't always look safe to let ->waiting remain set when returning from
functions that set it to point to stack area, since various locations check
for != NULL to see if it's valid.  So clear it on return from
ide_do_drive_cmd() and blk_execute_rq().

drivers/block/ll_rw_blk.c

@@ -1876,6 +1876,7 @@ int blk_execute_rq(request_queue_t *q, struct gendisk *bd_disk,
 	elv_add_request(q, rq, ELEVATOR_INSERT_BACK, 1);
 	generic_unplug_device(q);
 	wait_for_completion(&wait);
+	rq->waiting = NULL;
 
 	if (rq->errors)
 		err = -EIO;

drivers/ide/ide-io.c

@@ -1388,6 +1388,7 @@ int ide_do_drive_cmd (ide_drive_t *drive, struct request *rq, ide_action_t actio
 	err = 0;
 	if (must_wait) {
 		wait_for_completion(&wait);
+		rq->waiting = NULL;
 		if (rq->errors)
 			err = -EIO;