linux-kernel - Re: [PATCH] Default enable RCU list lockdep debugging with PROVE

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Message-ID: <20200228143751.GJ2935@paulmck-ThinkPad-P72>
Date:   Fri, 28 Feb 2020 06:37:51 -0800
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Joel Fernandes <joel@...lfernandes.org>
Cc:     madhuparnabhowmik10@...il.com, josh@...htriplett.org,
        rostedt@...dmis.org, mathieu.desnoyers@...icios.com,
        jiangshanlai@...il.com, linux-kernel@...r.kernel.org,
        Amol Grover <frextrite@...il.com>
Subject: Re: [PATCH] Default enable RCU list lockdep debugging with PROVE_RCU

On Fri, Feb 28, 2020 at 09:21:22AM -0500, Joel Fernandes wrote:
> On Fri, Feb 28, 2020 at 02:54:51PM +0530, madhuparnabhowmik10@...il.com wrote:
> > From: Madhuparna Bhowmik <madhuparnabhowmik10@...il.com>
> > 
> > This patch default enables CONFIG_PROVE_RCU_LIST option with
> > CONFIG_PROVE_RCU for RCU list lockdep debugging.
> > 
> > With this change, RCU list lockdep debugging will be default
> > enabled in CONFIG_PROVE_RCU=y kernels.
> > 
> > Most of the RCU users (in core kernel/, drivers/, and net/
> > subsystem) have already been modified to include lockdep
> > expressions hence RCU list debugging can be enabled by
> > default.
> > 
> > However, there are still chances of enountering
> > false-positive lockdep splats because not everything is converted,
> > in case RCU list primitives are used in non-RCU read-side critical
> > section but under the protection of a lock. It would be okay to
> > have a few false-positives, as long as bugs are identified, since this
> > patch only affects debugging kernels.
> > 
> > Co-developed-by: Amol Grover <frextrite@...il.com>
> > Signed-off-by: Amol Grover <frextrite@...il.com>
> > Signed-off-by: Madhuparna Bhowmik <madhuparnabhowmik10@...il.com>
> 
> Acked-by: Joel Fernandes (Google) <joel@...lfernandes.org>

Queued, thank you both!

							Thanx, Paul

> thanks,
> 
>  - Joel
> 
> > ---
> >  kernel/rcu/Kconfig.debug | 11 +++--------
> >  1 file changed, 3 insertions(+), 8 deletions(-)
> > 
> > diff --git a/kernel/rcu/Kconfig.debug b/kernel/rcu/Kconfig.debug
> > index 4aa02eee8f6c..ec4bb6c09048 100644
> > --- a/kernel/rcu/Kconfig.debug
> > +++ b/kernel/rcu/Kconfig.debug
> > @@ -9,15 +9,10 @@ config PROVE_RCU
> >  	def_bool PROVE_LOCKING
> >  
> >  config PROVE_RCU_LIST
> > -	bool "RCU list lockdep debugging"
> > -	depends on PROVE_RCU && RCU_EXPERT
> > -	default n
> > +	def_bool PROVE_RCU
> >  	help
> > -	  Enable RCU lockdep checking for list usages. By default it is
> > -	  turned off since there are several list RCU users that still
> > -	  need to be converted to pass a lockdep expression. To prevent
> > -	  false-positive splats, we keep it default disabled but once all
> > -	  users are converted, we can remove this config option.
> > +	  Enable RCU lockdep checking for list usages. It is default
> > +	  enabled with CONFIG_PROVE_RCU.
> >  
> >  config TORTURE_TEST
> >  	tristate
> > -- 
> > 2.17.1
> >