Re: Write barriers on MD RAID1

[Neil Brown <neilb@suse.de>]

On Sunday June 21, ken.milmore@googlemail.com wrote:
> I thought I had better bump my previous post as this regression is still 
> present in 2.6.29.5.

Thanks Ken.

> 
> To recap, commit cec0707e40ae25794b5a2de7b7f03c51961f80d9 has broken 
> write barriers on md raid1 block devices in 2.6.29 and later kernels. 
> Reversing this commit appears to fix the problem.
> 
> Please let me know if I'm harassing the wrong maintainers here!

Jens,
  have you had a chance to look at this?

I think the following patch is appropriate and should go in to
-stable.

Thanks,
NeilBrown


From addd8b129835a63d6df9a38eae20caaa15de5988 Mon Sep 17 00:00:00 2001
From: NeilBrown <neilb@suse.de>
Date: Wed, 24 Jun 2009 13:39:15 +1000
Subject: [PATCH] Restore barrier support for md and probably other virtual devices.

The next_ordered flag is only meaningful for devices that use __make_request.
So move the test against next_ordered out of generic code and in to
__make_request

Since this test was added, barriers have not worked on md, and (I
think) dm and similar devices that don't use __make_request and so
don't bother to set next_ordered.

Cc: stable@kernel.org
Cc: Ken Milmore <ken.milmore@googlemail.com>
Signed-off-by: NeilBrown <neilb@suse.de>
---
 block/blk-core.c |   10 +++++-----
 1 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index b06cf5c..fc221aa 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1172,6 +1172,11 @@ static int __make_request(struct request_queue *q, struct bio *bio)
 	const int unplug = bio_unplug(bio);
 	int rw_flags;
 
+	if (bio_barrier(bio) && bio_has_data(bio) &&
+	    (q->next_ordered == QUEUE_ORDERED_NONE)) {
+		bio_endio(bio, -EOPNOTSUPP)
+			return 0;
+	}
 	/*
 	 * low level driver can indicate that it wants pages above a
 	 * certain limit bounced to low memory (ie for highmem, or even
@@ -1472,11 +1477,6 @@ static inline void __generic_make_request(struct bio *bio)
 			err = -EOPNOTSUPP;
 			goto end_io;
 		}
-		if (bio_barrier(bio) && bio_has_data(bio) &&
-		    (q->next_ordered == QUEUE_ORDERED_NONE)) {
-			err = -EOPNOTSUPP;
-			goto end_io;
-		}
 
 		ret = q->make_request_fn(q, bio);
 	} while (ret);
-- 
1.6.3.1