linux-kernel - Re: Regression in 4.6.0-git - bisected to commit dd254f5a382c

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Message-ID: <20160525012805.GC14480@ZenIV.linux.org.uk>
Date:	Wed, 25 May 2016 02:28:05 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Matthew McClintock <mmcclint@...eaurora.org>
Cc:	Larry Finger <Larry.Finger@...inger.net>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: Regression in 4.6.0-git - bisected to commit dd254f5a382c

On Tue, May 24, 2016 at 08:20:46PM -0500, Matthew McClintock wrote:
> 
> > On May 24, 2016, at 8:10 PM, Al Viro <viro@...IV.linux.org.uk> wrote:
> > 
> > Slap the WARN_ON(!size); in the very beginning of iov_iter_advance(), see
> > where it's triggered...
> 
> diff --git a/lib/iov_iter.c b/lib/iov_iter.c
> index 28cb431..d89e154 100644
> --- a/lib/iov_iter.c
> +++ b/lib/iov_iter.c
> @@ -488,6 +488,7 @@ EXPORT_SYMBOL(iov_iter_copy_from_user_atomic);
> 
>  void iov_iter_advance(struct iov_iter *i, size_t size)
>  {
> +       WARN_ON(!size);
>         iterate_and_advance(i, size, v, 0, 0, 0)
>  }
>  EXPORT_SYMBOL(iov_iter_advance);
> 
> [    1.359869] This architecture does not have kernel memory protection.
> init started: BusyBox v1.24.1 ()
> starting pid 78, tty '': '/etc/init.d/rcS'
> [    1.435863] random: udevadm urandom read with 0 bits of entropy available
> [    1.448116] ------------[ cut here ]------------
> [    1.448193] WARNING: CPU: 1 PID: 88 at lib/iov_iter.c:491 iov_iter_advance+0xf0/0x1b8

The next obvious question is which binary it is and what's the return
address to userland; make that
	if (!size)
		printk(KERN_ERR "crap in %s[%x]",
			current->comm,
			current_pt_regs()->rip);
(in the same place)