Re: multipath: I/O hanging forever

[Andrea Righi <righi.andrea@gmail.com>]

On Sat, Mar 12, 2016 at 09:47:23AM +0800, Ming Lei wrote:
> 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?

It works perfectly to me.

Thanks!
-Andrea

Tested-by: Andrea Righi <righi.andrea@gmail.com>

> 
> ---
> 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,