Re: [PATCH tip/core/rcu 10/20] rcu: Provide diagnostic option to slow down grace-period initialization

From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Paul Bolle <pebolle@tiscali.nl>
Cc: linux-kernel@vger.kernel.org, mingo@kernel.org,
	laijs@cn.fujitsu.com, dipankar@in.ibm.com,
	akpm@linux-foundation.org, mathieu.desnoyers@efficios.com,
	josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org,
	rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com,
	dvhart@linux.intel.com, fweisbec@gmail.com, oleg@redhat.com,
	bobby.prani@gmail.com
Subject: Re: [PATCH tip/core/rcu 10/20] rcu: Provide diagnostic option to slow down grace-period initialization
Date: Wed, 4 Mar 2015 06:59:39 -0800	[thread overview]
Message-ID: <20150304145939.GK15405@linux.vnet.ibm.com> (raw)
In-Reply-To: <1425466477.2798.5.camel@tiscali.nl>

On Wed, Mar 04, 2015 at 11:54:37AM +0100, Paul Bolle wrote:
> All I spotted is a silly typo.
> 
> Paul E. McKenney schreef op di 03-03-2015 om 09:43 [-0800]:
> > --- a/lib/Kconfig.debug
> > +++ b/lib/Kconfig.debug
> > @@ -1257,6 +1257,30 @@ config RCU_TORTURE_TEST_RUNNABLE
> >  	  Say N here if you want the RCU torture tests to start only
> >  	  after being manually enabled via /proc.
> >  
> > +config RCU_TORTURE_TEST_SLOW_INIT
> > +	bool "Slow down RCU grace-period initialization to expose races"
> > +	depends on RCU_TORTURE_TEST
> > +	help
> > +	  This option makes grace-period initialization block for a
> > +	  few jiffies between initializing each pair of consecutive
> > +	  rcu_node structures.	This helps to expose races involving
> > +	  grace-period initialization, in other words, it makes your
> > +	  kernel less stable.  It can also greatly increase grace-period
> > +	  latency, especially on systems with large numbers of CPUs.
> > +	  This is useful when torture-testing RCU, but in almost no
> > +	  other circumstance.
> > +
> > +	  Say Y here if you want your system to crash and hang more often.
> 
> (Did you ever consider going into marketing?)

"Get your cold dead fish here!!!  And what is this 'sashimi' you speak of?"

But yes, I really do not want distros to enable this one.  Unless it
is some sort of Ridiculously Unstable Linux distro.  ;-)

> > +	  Say N if you want a sane system.
> > +
> > +config RCU_TORTURE_TEST_SLOW_INIT_DELAY
> > +	int "How must to slow down RCU grace-period initialization"
> 
> s/must/much/

Good catch, fixed!

							Thanx, Paul

> > +	range 0 5
> > +	default 0
> > +	help
> > +	  This option specifies the number of jiffies to wait between
> > +	  each rcu_node structure initialization.
> > +
> >  config RCU_CPU_STALL_TIMEOUT
> >  	int "RCU CPU stall timeout in seconds"
> >  	depends on RCU_STALL_COMMON
> 
> 
> Paul Bolle
> 