Re: 3.6-rc5 cgroups blkio throttle + md regression

[Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>]

On Thu, Sep 20, 2012 at 03:17:16PM -0400, Vivek Goyal wrote:
> I suspect we are looping in retry code because bio based queues never come
> out of bypass mode.
> 
>                 /*
>                  * If queue was bypassing, we should retry.  Do so after a
>                  * short msleep().  It isn't strictly necessary but queue
>                  * can be bypassing for some time and it's always nice to
>                  * avoid busy looping.
>                  */
>                 if (ret == -EBUSY) {
>                         msleep(10);
>                         ret = restart_syscall();
>                 }

Yeah, I incorrectly assumed that bio based drivers would call
blk_init_allocated_queue().  I think we need to move the initial
bypass_end call to blk_register_queue().  Like the following.  Not
completely sure yet tho.

diff --git a/block/blk-core.c b/block/blk-core.c
index 4b4dbdf..cbb019a 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -714,9 +714,6 @@ blk_init_allocated_queue(struct request_queue *q, request_fn_proc *rfn,
 		return NULL;
 
 	blk_queue_congestion_threshold(q);
-
-	/* all done, end the initial bypass */
-	blk_queue_bypass_end(q);
 	return q;
 }
 EXPORT_SYMBOL(blk_init_allocated_queue);
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index 9628b29..f53802e 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -527,6 +527,8 @@ int blk_register_queue(struct gendisk *disk)
 	if (WARN_ON(!q))
 		return -ENXIO;
 
+	blk_queue_bypass_end(q);
+
 	ret = blk_trace_init_sysfs(dev);
 	if (ret)
 		return ret;