linux-kernel - Re: iov_iter

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Date:   Tue, 11 Apr 2017 01:22:15 +0100
From:   Al Viro <viro@...IV.linux.org.uk>
To:     Dave Jones <davej@...emonkey.org.uk>,
        Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: iov_iter_pipe warning.

On Mon, Apr 10, 2017 at 07:48:30PM -0400, Dave Jones wrote:
>  > 	if (WARN_ON(pipe->nr_bufs))
>  > 		printk(KERN_ERR "->splice_write = %p",
>  > 			sd->u.file->f_op->splice_write);
>  > and see which function it is?
> 
> s/nr_bufs/nrbufs/ aside, I tried this, and it didn't trigger, even
> though I hit the iov_iter_pipe WARN again.

Huh?  So you have WARN_ON(pipe->nrbufs == pipe->buffers) trigger depite
WARN_ON(pipe->nrbufs) *not* triggering a bit earlier?  Nuts...

Let's do this:
	* in generic_file_splice_read(): WARN_ON(pipe->nrbufs == pipe->buffers)
*and* WARN_ON(!pipe->buffers) in the very beginning.
	* in do_splice_to(): ditto.
	* in splice_direct_to_actor(): if (WARN_ON... from upthread (with the
typo fix, of course).
	* in iov_iter_pipe() turn the test into
	if (WARN_ON(pipe->nrbufs == pipe->buffers))
		WARN_ON(pipe != current->splice_pipe);