Re: [tip:locking/urgent] locking/lockdep: Disable cross-release features for now

[Byungchul Park]

On Sat, Oct 14, 2017 at 04:36:51AM -0700, tip-bot for Ingo Molnar wrote:
> Commit-ID:  b483cf3bc249d7af706390efa63d6671e80d1c09
> Gitweb:     https://git.kernel.org/tip/b483cf3bc249d7af706390efa63d6671e80d1c09
> Author:     Ingo Molnar <mingo@xxxxxxxxxx>
> AuthorDate: Sat, 14 Oct 2017 09:26:59 +0200
> Committer:  Ingo Molnar <mingo@xxxxxxxxxx>
> CommitDate: Sat, 14 Oct 2017 12:50:26 +0200
> 
> locking/lockdep: Disable cross-release features for now
> 
> Johan Hovold reported a big lockdep slowdown on his system, caused by lockdep:
> 
> > I had noticed that the BeagleBone Black boot time appeared to have
> > increased significantly with 4.14 and yesterday I finally had time to
> > investigate it.
> >
> > Boot time (from "Linux version" to login prompt) had in fact doubled
> > since 4.13 where it took 17 seconds (with my current config) compared to
> > the 35 seconds I now see with 4.14-rc4.
> >
> > I quick bisect pointed to lockdep and specifically the following commit:
> >
> >	28a903f63ec0 ("locking/lockdep: Handle non(or multi)-acquisition of a crosslock")
> 
> Because the final v4.14 release is close, disable the cross-release lockdep
> features for now.
> 
> Bisected-by: Johan Hovold <johan@xxxxxxxxxx>
> Debugged-by: Johan Hovold <johan@xxxxxxxxxx>
> Reported-by: Johan Hovold <johan@xxxxxxxxxx>
> Cc: Arnd Bergmann <arnd@xxxxxxxx>
> Cc: Byungchul Park <byungchul.park@xxxxxxx>
> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Tony Lindgren <tony@xxxxxxxxxxx>
> Cc: kernel-team@xxxxxxx
> Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
> Cc: linux-mm@xxxxxxxxx
> Cc: linux-omap@xxxxxxxxxxxxxxx
> Link: http://lkml.kernel.org/r/20171014072659.f2yr6mhm5ha3eou7@xxxxxxxxx
> Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
> ---
>  lib/Kconfig.debug | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index 2689b7c..e270584 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -1092,8 +1092,8 @@ config PROVE_LOCKING
>  	select DEBUG_MUTEXES
>  	select DEBUG_RT_MUTEXES if RT_MUTEXES
>  	select DEBUG_LOCK_ALLOC
> -	select LOCKDEP_CROSSRELEASE
> -	select LOCKDEP_COMPLETIONS
> +	select LOCKDEP_CROSSRELEASE if BROKEN
> +	select LOCKDEP_COMPLETIONS if BROKEN

I agree with disabling crossrelease as default, becasue of regression,
as I originally did.

However, it's expected to spend more time once it's enabled. Is the
following acceptable?

----->8-----