Re: [ 103/133] xtensa: Add missing RCU idle APIs on idle loop

Chris Zankel
2012-10-11T00:30:38Z

Hi Greg,
Thanks for adding it.

Signed-off-by: Chris Zankel <chris@zankel.net>

On 10/10/2012 03:52 PM, Greg Kroah-Hartman wrote:
> 3.5-stable review patch. If anyone has any objections, please let me know.
>
> ------------------
>
> From: Frederic Weisbecker <fweisbec@gmail.com>
>
> commit 11ad47a0edbd62bfc0547cfcdf227a911433f207 upstream.
>
> 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>
> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
>
> ---
> arch/xtensa/kernel/process.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> --- 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();
> }
> }
>
>