linux-kernel - Re: Regression in kernel 4.12-rc1 for Powerpc 32

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Message-ID: <20170625111404.GV10672@ZenIV.linux.org.uk>
Date:   Sun, 25 Jun 2017 12:14:04 +0100
From:   Al Viro <viro@...IV.linux.org.uk>
To:     Larry Finger <Larry.Finger@...inger.net>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Thorsten Leemhuis <regressions@...mhuis.info>,
        linuxppc-dev@...ts.ozlabs.org
Subject: Re: Regression in kernel 4.12-rc1 for Powerpc 32 - bisected to
 commit 3448890c32c3

On Sun, Jun 25, 2017 at 10:53:58AM +0100, Al Viro wrote:
> On Sat, Jun 24, 2017 at 12:29:23PM -0500, Larry Finger wrote:
> 
> > I made a break through. If I turn off inline copy to/from users for 32-bit
> > ppc with the following patch, then the system boots:
> 
> OK...  So it's 4.6.3 miscompiling something - it is hardware-independent,
> reproduced in qemu.  I'd like to get more self-contained example of
> miscompile, though; should be done by tonight...

OK, it's the call in rw_copy_check_uvector(); with INLINE_COPY_FROM_USER
it's miscompiled by 4.6.3.  I hadn't looked through the generated code
yet; will do that after I grab some sleep.