linux-kernel - Re: iov_iter

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Date:   Mon, 10 Apr 2017 20:28:00 +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 Tue, Mar 21, 2017 at 04:59:01PM -0400, Dave Jones wrote:
> WARNING: CPU: 0 PID: 9290 at lib/iov_iter.c:836 iov_iter_pipe+0x71/0x80
> CPU: 0 PID: 9290 Comm: trinity-c7 Not tainted 4.11.0-rc3-think+ #3 
> Call Trace:
>  dump_stack+0x68/0x93
>  __warn+0xcb/0xf0
>  warn_slowpath_null+0x1d/0x20
>  iov_iter_pipe+0x71/0x80
>  generic_file_splice_read+0x37/0x140
>  do_splice_to+0x79/0x90
>  splice_direct_to_actor+0xb8/0x220
>  ? generic_pipe_buf_nosteal+0x10/0x10
>  do_splice_direct+0x9e/0xd0
>  do_sendfile+0x1d7/0x3c0
>  SyS_sendfile64+0x73/0xe0
>  do_syscall_64+0x66/0x1d0

Cute...  We have ->splice_read() called in attempt to shove something into
a full internal pipe.  How do you achieve that situation?  actor() callback
claiming to have drained more than it actually had to?

Do you have a reliable reproducer?