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SubjectRe: iov_iter_pipe warning.
On Thu, Sep 07, 2017 at 09:46:17AM +1000, Dave Chinner wrote:
> 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....

The puzzling part is this runs for a day on ext4 or btrfs, whereas I can
make xfs fall over pretty quickly. As Darrick pointed out though, this
could be due to xfs being the only user of iomap_dio_rw.

I'm juggling a few other things right now, so probably not going to
have much time to dig further on this until after plumbers + 1 wk.

Dave

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