From: Neil Brown <neilb@cse.unsw.edu.au>
To: Andrew Morton <akpm@osdl.org>
Date: Sat, 9 Aug 2003 10:39:43 +1000
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Message-ID: <16180.17103.360112.493943@gargle.gargle.HOWL>
Cc: dan@debian.org, linux-kernel@vger.kernel.org, ext3-users@redhat.com
Subject: Re: ext3 badness in 2.6.0-test2
In-Reply-To: message from Andrew Morton on Thursday August 7
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On Thursday August 7, akpm@osdl.org wrote:
> Neil Brown <neilb@cse.unsw.edu.au> wrote:
> 
> > So I guess the finger points generally in the direction of raid5.
> > Now I've just got to figure if it is a bug in r5, or some assumption
> > that it makes that is no longer valid (I was briefly suspicious of
> > PF_READAHEAD which could have made a real mess of raid5, but that
> > wouldn't have this symptom)
> 
> The PF_READAHEAD things was a huge bug.  Make sure that it is fixed before
> proceeding.  Linus's tree has the fix.

I found it. It was read-ahead related, but nothing to do with
PF_READAHEAD.

With this patch, my test ran to completion instead of dying at about
th 20% mark.

NeilBrown

=================================================================
Disable raid5 handling of read-ahead

raid5 trys to honour RWA_MASK, but messes it up and can return bad data.
Just ignore RWA_MASK for now.


 ----------- Diffstat output ------------
 ./drivers/md/raid5.c |    2 +-
 1 files changed, 1 insertion(+), 1 deletion(-)

diff ./drivers/md/raid5.c~current~ ./drivers/md/raid5.c
--- ./drivers/md/raid5.c~current~	2003-08-08 14:37:00.000000000 +1000
+++ ./drivers/md/raid5.c	2003-08-08 14:37:19.000000000 +1000
@@ -1326,7 +1326,7 @@ static int make_request (request_queue_t
 			(unsigned long long)new_sector, 
 			(unsigned long long)logical_sector);
 
-		sh = get_active_stripe(conf, new_sector, pd_idx, (bi->bi_rw&RWA_MASK));
+		sh = get_active_stripe(conf, new_sector, pd_idx, 0/*(bi->bi_rw&RWA_MASK)*/);
 		if (sh) {
 
 			add_stripe_bio(sh, bi, dd_idx, (bi->bi_rw&RW_MASK));


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