Re: [PATCH 4.19 000/219] 4.19.92-stable review

[Guenter Roeck]

On 1/1/20 8:24 AM, Greg Kroah-Hartman wrote:
> On Tue, Dec 31, 2019 at 06:01:12PM -0800, Guenter Roeck wrote:
> > On 12/30/19 9:35 AM, Greg Kroah-Hartman wrote:
> > > On Mon, Dec 30, 2019 at 09:19:59AM -0800, Guenter Roeck wrote:
> > > > On Sun, Dec 29, 2019 at 06:16:42PM +0100, Greg Kroah-Hartman wrote:
> > > > > This is the start of the stable review cycle for the 4.19.92 release.
> > > > > There are 219 patches in this series, all will be posted as a response
> > > > > to this one.  If anyone has any issues with these being applied, please
> > > > > let me know.
> > > > >
> > > > > Responses should be made by Tue, 31 Dec 2019 16:17:25 +0000.
> > > > > Anything received after that time might be too late.
> > > > Build results:
> > > > 	total: 156 pass: 141 fail: 15
> > > > Failed builds:
> > > > 	i386:tools/perf
> > > > 	<all mips>
> > > > 	x86_64:tools/perf
> > > > Qemu test results:
> > > > 	total: 381 pass: 316 fail: 65
> > > > Failed tests:
> > > > 	<all mips>
> > > > 	<all ppc64_book3s_defconfig>
> > > >
> > > > perf as with v4.14.y.
> > > >
> > > > arch/mips/kernel/syscall.c:40:10: fatal error: asm/sync.h: No such file or directory
> > >
> > > Ah, will go drop the offending patch and push out a -rc2 with both of
> > > these issues fixed.
> > >
> > > > arch/powerpc/include/asm/spinlock.h:56:1: error: type defaults to âintâ in declaration of âDECLARE_STATIC_KEY_FALSEâ
> > > > and similar errors.
> > > >
> > > > The powerpc build problem is inherited from mainline and has not been fixed
> > > > there as far as I can see. I guess that makes 4.19.y bug-for-bug "compatible"
> > > > with mainline in that regard.
> > >
> > > bug compatible is fun :(
> >
> > Not really. It is a terrible idea and results in the opposite of what I would
> > call a "stable" release.
> >
> > Anyway, turns out the offending commit is 14c73bd344d ("powerpc/vcpu: Assume
> > dedicated processors as non-preempt"), which uses static_branch_unlikely().
>
> It does?  I see:
>
> +               if (lppaca_shared_proc(get_lppaca()))
> +                       static_branch_enable(&shared_processor);
>
> > This function does not exist for ppc in v4.19.y and v5.4.y. Thus, the _impact_
> > of the error in v4.19.y and v5.4.y is the same as in mainline, but the _cause_
> > is different. Upstream commit 14c73bd344d should not have been applied to
> > v4.19.y and v5.4.y and needs to be reverted from those branches.
>
> I'll go revert this patch, but as it was marked for stable by the
> authors of the patch, as relevant back to 4.18, I would have hoped that
> they knew what they were doing :)

I probably didn't have enough champagne last night when I wrote my previous e-mail.
No, the problem is the same as with the upstream kernel, so feel free to drop
the revert if you prefer "bug-for-bug compatibility". Given where we are, that
is probably better than dropping the patch and re-applying it after its fix
is available.

The underlying problem is that the offending patch introduces the use of
jump label code into arch/powerpc/include/asm/spinlock.h without including
linux/jump_label.h. Depending on the configuration, this results in the observed
build errors.

Patches were submitted upstream to fix the problem, but the fix has not been
applied to mainline, and I don't see a maintainer reaction. Maybe everyone
is off for the holidays.

https://patchwork.ozlabs.org/patch/1215380/
https://patchwork.ozlabs.org/patch/1214954/

Guenter