[RFC]md: using GFP_NOIO to allocate bio for flush request

[Shaohua Li <shli@kernel.org>]

flush request is issued in transaction commit code path usually, so 
looks using
GFP_KERNEL to allocate memory for flush request bio falls into the classic
deadlock issue. dm already gets it right.

Signed-off-by: Shaohua Li <shli@fusionio.com>
---
  drivers/md/md.c |    2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

Index: linux/drivers/md/md.c
===================================================================
--- linux.orig/drivers/md/md.c	2012-04-13 10:03:58.395497650 +0800
+++ linux/drivers/md/md.c	2012-04-13 10:04:37.445497882 +0800
@@ -450,7 +450,7 @@ static void submit_flushes(struct work_s
  			atomic_inc(&rdev->nr_pending);
  			atomic_inc(&rdev->nr_pending);
  			rcu_read_unlock();
-			bi = bio_alloc_mddev(GFP_KERNEL, 0, mddev);
+			bi = bio_alloc_mddev(GFP_NOIO, 0, mddev);
  			bi->bi_end_io = md_end_flush;
  			bi->bi_private = rdev;
  			bi->bi_bdev = rdev->bdev;