linux-kernel - Re: [PATCH tip/core/rcu 1/2] rcu: Provide RCU CPU stall warnings for tiny RCU

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Date:	Sun, 27 Jan 2013 21:57:08 +1100
From:	Josh Triplett <josh@...htriplett.org>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com,
	dipankar@...ibm.com, akpm@...ux-foundation.org,
	mathieu.desnoyers@...ymtl.ca, niv@...ibm.com, tglx@...utronix.de,
	peterz@...radead.org, rostedt@...dmis.org, Valdis.Kletnieks@...edu,
	dhowells@...hat.com, edumazet@...gle.com, darren@...art.com,
	fweisbec@...il.com, sbw@....edu,
	"Paul E. McKenney" <paul.mckenney@...aro.org>
Subject: Re: [PATCH tip/core/rcu 1/2] rcu: Provide RCU CPU stall warnings for
 tiny RCU

On Sat, Jan 26, 2013 at 04:23:46PM -0800, Paul E. McKenney wrote:
> From: "Paul E. McKenney" <paul.mckenney@...aro.org>
> 
> Tiny RCU has historically omitted RCU CPU stall warnings in order to
> reduce memory requirements, however, lack of these warnings caused
> Thomas Gleixner some debugging pain recently.  Therefore, this commit
> adds RCU CPU stall warnings to tiny RCU if RCU_TRACE=y.  This keeps
> the memory footprint small, while still enabling CPU stall warnings
> in kernels built to enable them.
> 
> Updated to include Josh Triplett's suggested use of RCU_STALL_COMMON
> config variable to simplify #if expressions.
> 
> Reported-by: Thomas Gleixner <tglx@...utronix.de>
> Signed-off-by: Paul E. McKenney <paul.mckenney@...aro.org>
> Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>

One suggestion below; with that change,
Reviewed-by: Josh Triplett <josh@...htriplett.org>

> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -486,6 +486,14 @@ config PREEMPT_RCU
>  	  This option enables preemptible-RCU code that is common between
>  	  the TREE_PREEMPT_RCU and TINY_PREEMPT_RCU implementations.
>  
> +config RCU_STALL_COMMON
> +	def_bool ( TREE_RCU || TREE_PREEMPT_RCU || RCU_TRACE )
> +	help
> +	  This option enables RCU CPU stall code that is common between
> +	  the TINY and TREE variants of RCU.  The purpose is to allow
> +	  the tiny variants to disable RCU CPU stall warnings, while
> +	  making these warnings mandatory for the tree variants.
> +
[...]
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -970,7 +970,7 @@ config RCU_TORTURE_TEST_RUNNABLE
>  
>  config RCU_CPU_STALL_TIMEOUT
>  	int "RCU CPU stall timeout in seconds"
> -	depends on TREE_RCU || TREE_PREEMPT_RCU
> +	depends on TREE_RCU || TREE_PREEMPT_RCU || RCU_TRACE

depends on RCU_STALL_COMMON
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