linux-kernel - Re: blktrace/relay/s390: Oops in subbuf_splice

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Message-ID: <20080423070850.GV12774@kernel.dk>
Date:	Wed, 23 Apr 2008 09:08:50 +0200
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Christof Schmitt <christof.schmitt@...ibm.com>
Cc:	Tom Zanussi <zanussi@...cast.net>, linux-btrace@...r.kernel.org,
	linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
	wilder@...ibm.com
Subject: Re: blktrace/relay/s390: Oops in subbuf_splice_actor

On Wed, Apr 23 2008, Christof Schmitt wrote:
> On Mon, Apr 07, 2008 at 11:23:07PM -0500, Tom Zanussi wrote:
> > > Dave, can you have a look at this? I can easily reproduce the problem
> > > on s390 Linux for testing and getting more debug information.
> > > 
> > 
> > Not sure anyone's still looking into this, but it doesn't look like an
> > s390 problem specifically.  Apparently what happened was that some
> > internal changes to splice seem to have broken the relay splice_read
> > implementation.  The above patch fixes part of the problem; the patch
> > below should fix the rest, and AFAICT it doesn't break anything else.
> > 
> > Signed-off-by: Tom Zanussi <zanussi@...cast.net>
> > 
> > diff --git a/fs/splice.c b/fs/splice.c
> > index a861bb3..068b210 100644
> > --- a/fs/splice.c
> > +++ b/fs/splice.c
> > @@ -1094,7 +1094,7 @@ long do_splice_direct(struct file *in, loff_t *ppos, struct file *out,
> > 
> >  	ret = splice_direct_to_actor(in, &sd, direct_splice_actor);
> >  	if (ret > 0)
> > -		*ppos += ret;
> > +		*ppos = sd.pos;
> > 
> >  	return ret;
> >  }
> > diff --git a/kernel/relay.c b/kernel/relay.c
> > index d6204a4..dc873fb 100644
> > --- a/kernel/relay.c
> > +++ b/kernel/relay.c
> > @@ -1162,7 +1162,7 @@ static ssize_t relay_file_splice_read(struct file *in,
> >  	ret = 0;
> >  	spliced = 0;
> > 
> > -	while (len) {
> > +	while (len && !spliced) {
> >  		ret = subbuf_splice_actor(in, ppos, pipe, len, flags, &nonpad_ret);
> >  		if (ret < 0)
> >  			break;
> > 
> > 
> 
> Sorry for the late response and yes, our tests on s390 are still
> tracking the issue. I just ran a short test on 2.6.25 with the above
> patch applied. With this patch, blktrace client/server mode works
> again with the sendfile() call and returns valid data for blkparse.
> 
> Thanks everybody for helping with this problem.
> 
> Jens, will you pick up this patch for inclusion?

Certainly, thanks to Tom for providing this and you for testing!

-- 
Jens Axboe

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