On Wed, Aug 22, 2012 at 06:23:39PM +0200, Frederic Weisbecker wrote:
> 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 Alpha's idle loop.
>
> Reported-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
> Signed-off-by: Frederic Weisbecker <fweisbec@xxxxxxxxx>
> Cc: Richard Henderson <rth@xxxxxxxxxxx>
> Cc: Ivan Kokshaysky <ink@xxxxxxxxxxxxxxxxxxxx>
> Cc: Matt Turner <mattst88@xxxxxxxxx>
> Cc: alpha <linux-alpha@xxxxxxxxxxxxxxx>
> Cc: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
> Cc: 3.2.x.. <stable@xxxxxxxxxx>
> ---
> arch/alpha/kernel/process.c | 6 +++++-
> 1 files changed, 5 insertions(+), 1 deletions(-)
>
> diff --git a/arch/alpha/kernel/process.c b/arch/alpha/kernel/process.c
> index 153d3fc..2ebf7b5 100644
> --- a/arch/alpha/kernel/process.c
> +++ b/arch/alpha/kernel/process.c
> @@ -28,6 +28,7 @@
> #include <linux/tty.h>
> #include <linux/console.h>
> #include <linux/slab.h>
> +#include <linux/rcupdate.h>
>
> #include <asm/reg.h>
> #include <asm/uaccess.h>
> @@ -50,13 +51,16 @@ cpu_idle(void)
> {
> set_thread_flag(TIF_POLLING_NRFLAG);
>
> + preempt_disable();
I don't understand the above preempt_disable() not having a matching
preempt_enable() at exit, but the rest of the patches in this series
look good to me.
Thanx, Paul
> while (1) {
> /* FIXME -- EV6 and LCA45 know how to power down
> the CPU. */
>
> + rcu_idle_enter();
> while (!need_resched())
> cpu_relax();
> - schedule();
> + rcu_idle_exit();
> + schedule_preempt_disabled();
> }
> }
>
> --
> 1.7.5.4
>
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