linux-kernel - Re: iov_iter

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Message-ID: <20170410194206.loesu5licstif7or@codemonkey.org.uk>
Date:   Mon, 10 Apr 2017 15:42:06 -0400
From:   Dave Jones <davej@...emonkey.org.uk>
To:     Al Viro <viro@...IV.linux.org.uk>
Cc:     Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: iov_iter_pipe warning.

On Mon, Apr 10, 2017 at 08:28:00PM +0100, Al Viro wrote:
 > 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?

Not reliable, but I'll see if I can find some time to narrow it down
this week.  I've been working on better logging of "wtf just happened"
the last few weeks, so it should get easier once I finish that work.

	Dave