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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Date:	Wed, 14 Jul 2010 14:16:06 -0700
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, 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 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.

- Josh Triplett
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