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

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Message-ID: <20080314132238.GA9815@schmichrtp.de.ibm.com>
Date:	Fri, 14 Mar 2008 14:22:39 +0100
From:	Christof Schmitt <christof.schmitt@...ibm.com>
To:	Jens Axboe <jens.axboe@...cle.com>
Cc:	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 Fri, Mar 14, 2008 at 02:10:07PM +0100, Jens Axboe wrote:
> On Fri, Mar 14 2008, Christof Schmitt wrote:
> > On Fri, Mar 14, 2008 at 12:58:03PM +0100, Jens Axboe wrote:
> > > That is indeed a bug, does this work for you?
> > > 
> > > diff --git a/kernel/relay.c b/kernel/relay.c
> > > index d080b9d..39d1fa8 100644
> > > --- a/kernel/relay.c
> > > +++ b/kernel/relay.c
> > > @@ -1066,7 +1066,7 @@ static int subbuf_splice_actor(struct file *in,
> > >  			       unsigned int flags,
> > >  			       int *nonpad_ret)
> > >  {
> > > -	unsigned int pidx, poff, total_len, subbuf_pages, ret;
> > > +	unsigned int pidx, poff, total_len, subbuf_pages, nr_pages, ret;
> > >  	struct rchan_buf *rbuf = in->private_data;
> > >  	unsigned int subbuf_size = rbuf->chan->subbuf_size;
> > >  	uint64_t pos = (uint64_t) *ppos;
> > > @@ -1098,7 +1098,9 @@ static int subbuf_splice_actor(struct file *in,
> > >  	pidx = (read_start / PAGE_SIZE) % subbuf_pages;
> > >  	poff = read_start & ~PAGE_MASK;
> > > 
> > > -	for (total_len = 0; spd.nr_pages < subbuf_pages; spd.nr_pages++) {
> > > +	nr_pages = min_t(unsigned int, subbuf_pages, PIPE_BUFFERS);
> > > +
> > > +	for (total_len = 0; spd.nr_pages < nr_pages; spd.nr_pages++) {
> > >  		unsigned int this_len, this_end, private;
> > >  		unsigned int cur_pos = read_start + total_len;
> > 
> > With the patch, i can run dd and 'blktrace -h traceserver' without the
> > oops. But the output from blktrace only contains only zeros and no
> > usable data for blkparse. Using blktrace to write the data directly to
> > disk, without using the blktrace server works. Is there anything i
> > should look for to help debugging the problem?
> 
> We should probably get Tom in the loop, as he is the relay expert. I'll
> make sure the above patch gets into 2.6.25, as it is definitely a bug
> that needs fixing.

http://relayfs.sourceforge.net/contact.html mentions Tom Zanussi, but
his email address seems to be no longer valid. I copy Dave Wilder
here, since he is mentioned as relay maintainer on the web page.

Dave, can you have a look at this? I can easily reproduce the problem
on s390 Linux for testing and getting more debug information.

Christof
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