Re: [PATCH tip/core/rcu 25/26] xtensa: Add missing RCU idle APIs on idle loop

[Josh Triplett <josh@joshtriplett.org>]

On Thu, Aug 30, 2012 at 02:05:42PM -0700, Paul E. McKenney wrote:
> From: Frederic Weisbecker <fweisbec@gmail.com>
> 
> In the old times, the whole idle task was considered
> as an RCU quiescent state. But as RCU became more and
> more successful overtime, some RCU read side critical
> section have been added even in the code of some
> architectures idle tasks, for tracing for example.
> 
> So nowadays, rcu_idle_enter() and rcu_idle_exit() must
> be called by the architecture to tell RCU about the part
> in the idle loop that doesn't make use of rcu read side
> critical sections, typically the part that puts the CPU
> in low power mode.
> 
> This is necessary for RCU to find the quiescent states in
> idle in order to complete grace periods.
> 
> Add this missing pair of calls in the xtensa's idle loop.
> 
> Reported-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
> Cc: Chris Zankel <chris@zankel.net>
> Cc: 3.2.x.. <stable@vger.kernel.org>
> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

Reviewed-by: Josh Triplett <josh@joshtriplett.org>

>  arch/xtensa/kernel/process.c |    3 +++
>  1 files changed, 3 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/xtensa/kernel/process.c b/arch/xtensa/kernel/process.c
> index 2c8d6a3..bc44311 100644
> --- a/arch/xtensa/kernel/process.c
> +++ b/arch/xtensa/kernel/process.c
> @@ -31,6 +31,7 @@
>  #include <linux/mqueue.h>
>  #include <linux/fs.h>
>  #include <linux/slab.h>
> +#include <linux/rcupdate.h>
>  
>  #include <asm/pgtable.h>
>  #include <asm/uaccess.h>
> @@ -110,8 +111,10 @@ void cpu_idle(void)
>  
>  	/* endless idle loop with no priority at all */
>  	while (1) {
> +		rcu_idle_enter();
>  		while (!need_resched())
>  			platform_idle();
> +		rcu_idle_exit();
>  		schedule_preempt_disabled();
>  	}
>  }
> -- 
> 1.7.8
>