xfs_file_splice_read: possible circular locking dependency detected

[Linus Torvalds]

On Fri, Sep 2, 2016 at 5:39 PM, Dave Chinner <david at fromorbit.com> wrote:
>
> Fundamentally a splice infrastructure problem.

Yeah, I don't really like how we handle the pipe lock.

It *might* be possible to instead just increment the reference
counters as we build a kvec[] array of them, and simply do teh write
without holding the pipe lock at all.

That has other problems, ie concurrect spices from the same pipe would
possibly write the same data multiple times, though.

But yes, the fundamental problem is how splice wants to take the pipe
lock both early and late. Very annoying.

              Linus