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

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Date:	Fri, 14 Mar 2008 08:21:03 -0700
From:	David Wilder <dwilder@...ibm.com>
To:	Christof Schmitt <christof.schmitt@...ibm.com>
CC:	Jens Axboe <jens.axboe@...cle.com>, 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

Christof Schmitt wrote:
> 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 his email address seems to be no longer valid.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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I will take a look at the problem.
Any thing special about the test you are running I need to know?
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