Re: Odd build breakage in 4.9-rc7

From: Jarod Wilson
Date: Wed Nov 30 2016 - 14:01:02 EST

On 2016-11-30 1:50 PM, Prarit Bhargava wrote:

On 11/30/2016 01:36 PM, Linus Torvalds wrote:
On Wed, Nov 30, 2016 at 10:28 AM, Prarit Bhargava <prarit@xxxxxxxxxx> wrote:
In my case I tracked this to commit 3637efb00864 ("x86/mce: Add PCI quirks to
identify Xeons with machine check recovery") which adds the include for

Ok, that at least makes some sense. The other blamed commit did not
seem to possibly make a difference.

Searching LKML and I came across a report from Ken Moffat from a month ago:

Does a "make clean" get rid of it forever? Or does it come back?

It comes back. The steps to reproduce this are:

1. checkout latest linux.git
2. make -j112

(IOW, it occurs 100% of the time for me on a clean tree.)

To work around the bug I have to do

1. checkout latest linux.git
2. comment out the include for generated/autoksyms.h at include/linux/export.h:81
3. compile with -j112

This fails loudly, but then I do

4. uncomment the include for generated/autoksyms.h at include/linux/export.h:81
5. make -j112

and this completes with a bootable kernel AFAICT.

In my case, I first noticed this with rpm builds, which are unpacking a tarball every time. I did have ccache installed, but have removed it, to no avail. I still get this failure. Reverting these three patches...


...gets me a working build every time. So I'm not so sure these patches are completely innocent. They may not be directly at fault, but certainly seem to be involved in causing things to get tripped up.

If it's a one-time dependency issue that is because some header
dependency addition that the automatic dependency generator hadn't
caught, that might explain a bisection failure too: once the file
happens to get rebuilt (and the dependencies re-done), it starts
working even though the "happens to be rebuilt" had nothing to do with
the original bug.

Hopefully the linux-kbuild folks might be able to point us in the right
direction for a fix.

Indeed. I'm mostly clueless here. Well, mostly clueless, period, but even more so here. And with the CONFIG_MODVERSIONS part of my original mail, which I guess I should also re-test with ccache uninstalled...

Jarod Wilson