Re: [PATCH] Default enable RCU list lockdep debugging with PROVE_RCU

[Joel Fernandes]

On Fri, Feb 28, 2020 at 02:54:51PM +0530, madhuparnabhowmik10@xxxxxxxxx wrote:
> From: Madhuparna Bhowmik <madhuparnabhowmik10@xxxxxxxxx>
> 
> 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@xxxxxxxxx>
> Signed-off-by: Amol Grover <frextrite@xxxxxxxxx>
> Signed-off-by: Madhuparna Bhowmik <madhuparnabhowmik10@xxxxxxxxx>

Acked-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>

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
>