Re: multipath: I/O hanging forever

[Ming Lei <tom.leiming@gmail.com>]

On Fri, 11 Mar 2016 15:24:33 -0700
Andrea Righi <righi.andrea@gmail.com> wrote:

> On Sat, Mar 05, 2016 at 08:31:03PM -0900, Kent Overstreet wrote:
> > On Fri, Mar 04, 2016 at 10:30:44AM -0700, Andrea Righi wrote:
> > > On Sun, Feb 28, 2016 at 08:46:16PM -0700, Andrea Righi wrote:
> > > > On Sun, Feb 28, 2016 at 06:53:33PM -0700, Andrea Righi wrote:
> > > > ... 
> > > > > I'm using 4.5.0-rc5+, from Linus' git. I'll try to do a git bisect
> > > > > later, I'm pretty sure this problem has been introduced recently (i.e.,
> > > > > I've never seen this issue with 4.1.x).
> > > > 
> > > > I confirm, just tested kernel 4.1 and this problem doesn't happen.
> > > 
> > > Alright, I had some spare time to bisect this problem and I found that
> > > the commit that introduced this issue is c66a14d.
> > > 
> > > So, I tried to revert the commit (with some changes to fix conflicts and
> > > ABI changes) and now multipath seems to work fine for me (no hung task).
> > 
> > Is it hanging on first IO, first large IO, or just randomly?
> 
> It's always the very first O_DIRECT I/O, in general the task gets stuck
> in do_blockdev_direct_IO().

I can reproduce the issue too, and looks it is a MD issue instead of block.
Andrea, could you try the following patch to see if it can fix your issue?

---
From 43fc9c221e53c64f2df7c100c77cc25c4a98c607 Mon Sep 17 00:00:00 2001
From: Ming Lei <ming.lei@canonical.com>
Date: Sat, 12 Mar 2016 09:29:40 +0800
Subject: [PATCH] md: multipath: don't hardcopy bio in .make_request path

Inside multipath_make_request(), multipath maps the incoming
bio into low level device's bio, but it is totally wrong to
copy the bio into mapped bio via '*mapped_bio = *bio'. For
example, .__bi_remaining is kept in the copy, especially if
the incoming bio is chained to via bio splitting, so .bi_end_io
can't be called for the mapped bio at all in the completing path
in this kind of situation.

This patch fixes the issue by using clone style.

Signed-off-by: Ming Lei <ming.lei@canonical.com>
---
 drivers/md/multipath.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/md/multipath.c b/drivers/md/multipath.c
index 0a72ab6..dd483bb 100644
--- a/drivers/md/multipath.c
+++ b/drivers/md/multipath.c
@@ -129,7 +129,9 @@ static void multipath_make_request(struct mddev *mddev, struct bio * bio)
 	}
 	multipath = conf->multipaths + mp_bh->path;
 
-	mp_bh->bio = *bio;
+	bio_init(&mp_bh->bio);
+	__bio_clone_fast(&mp_bh->bio, bio);
+
 	mp_bh->bio.bi_iter.bi_sector += multipath->rdev->data_offset;
 	mp_bh->bio.bi_bdev = multipath->rdev->bdev;
 	mp_bh->bio.bi_rw |= REQ_FAILFAST_TRANSPORT;
-- 
1.9.1


Thanks,