linux-kernel - Re: [PATCH RFC tip/core/rcu 29/30] rcu: add boot parameter to suppress RCU CPU stall warning messages

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Message-ID: <20100714233029.GK2417@linux.vnet.ibm.com>
Date:	Wed, 14 Jul 2010 16:30:29 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Josh Triplett <josh@...htriplett.org>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com,
	dipankar@...ibm.com, akpm@...ux-foundation.org,
	mathieu.desnoyers@...ymtl.ca, dvhltc@...ibm.com, niv@...ibm.com,
	tglx@...utronix.de, peterz@...radead.org, rostedt@...dmis.org,
	Valdis.Kletnieks@...edu, dhowells@...hat.com,
	eric.dumazet@...il.com
Subject: Re: [PATCH RFC tip/core/rcu 29/30] rcu: add boot parameter to
 suppress RCU CPU stall warning messages

On Wed, Jul 14, 2010 at 02:16:06PM -0700, Josh Triplett wrote:
> On Wed, Jul 14, 2010 at 01:10:03PM -0700, Paul E. McKenney wrote:
> > Although the RCU CPU stall warning messages are a very good way to alert
> > people to a problem, once alerted, it is sometimes helpful to shut them
> > off in order to avoid obscuring other messages that might be being used
> > to track down the problem.  Although you can rebuild the kernel with
> > CONFIG_RCU_CPU_STALL_DETECTOR=n, this is sometimes inconvenient.  This
> > commit therefore adds a boot parameter named "rcu_cpu_stall_suppress"
> > that shuts these messages off without requiring a rebuild (though a
> > reboot might be needed for those not brave enough to patch their kernel
> > while it is running).
> > 
> > This message-suppression was already in place for the panic case, so this
> > commit need only rename the variable and export it via module_param().
> > 
> > Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> > ---
> >  kernel/rcutree.c |   11 ++++++++---
> >  1 files changed, 8 insertions(+), 3 deletions(-)
> > 
> > diff --git a/kernel/rcutree.c b/kernel/rcutree.c
> > index 5b1c3c2..f3d5906 100644
> > --- a/kernel/rcutree.c
> > +++ b/kernel/rcutree.c
> > @@ -143,6 +143,11 @@ module_param(blimit, int, 0);
> >  module_param(qhimark, int, 0);
> >  module_param(qlowmark, int, 0);
> >  
> > +#ifdef CONFIG_RCU_CPU_STALL_DETECTOR
> > +int rcu_cpu_stall_suppress __read_mostly;
> > +module_param(rcu_cpu_stall_suppress, int, 0);
> > +#endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
> 
> In theory, you could change the permissions on this module_param from 0
> to 0644, making it appear under /sys as a writable file.  That would
> allow changing it at runtime rather than just at boot time.  Looking at
> the use of this variable, changing it dynamically should work.

Will give it a try!

							Thanx, Paul
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