Re: iov_iter_pipe warning.

[Dave Chinner <david@fromorbit.com>]

On Wed, Sep 06, 2017 at 04:03:37PM -0400, Dave Jones wrote:
> On Mon, Aug 28, 2017 at 09:25:42PM -0700, Darrick J. Wong wrote:
>  > On Mon, Aug 28, 2017 at 04:31:30PM -0400, Dave Jones wrote:
>  > > I'm still trying to narrow down an exact reproducer, but it seems having
>  > > trinity do a combination of sendfile & writev, with pipes and regular
>  > > files as fd's is the best repro.
>  > > 
>  > > Is this a real problem, or am I chasing ghosts ?  That it doesn't happen
>  > > on ext4 or btrfs is making me wonder...
>  > 
>  > <shrug> I haven't heard of any problems w/ directio xfs lately, but OTOH
>  > I think it's the only filesystem that uses iomap_dio_rw, which would
>  > explain why ext4/btrfs don't have this problem.
> 
> Another warning, from likely the same root cause.
> 
> WARNING: CPU: 3 PID: 572 at lib/iov_iter.c:962 iov_iter_pipe+0xe2/0xf0

	WARN_ON(pipe->nrbufs == pipe->buffers);

 *      @nrbufs: the number of non-empty pipe buffers in this pipe
 *      @buffers: total number of buffers (should be a power of 2)

So that's warning that the pipe buffer is already full before we
try to read from the filesystem?

That doesn't seem like an XFS problem - it indicates the pipe we are
filling in generic_file_splice_read() is not being emptied by
whatever we are splicing the file data to....

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com