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

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Message-ID: <20080314131007.GQ17940@kernel.dk>
Date:	Fri, 14 Mar 2008 14:10:07 +0100
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Christof Schmitt <christof.schmitt@...ibm.com>
Cc:	linux-btrace@...r.kernel.org, linux-s390@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: blktrace/relay/s390: Oops in subbuf_splice_actor

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.

-- 
Jens Axboe

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