[PATCH tip/core/rcu 15/26] alpha: Fix preemption handling in idle loop

[PATCH tip/core/rcu 15/26] alpha: Fix preemption handling in idle loop

[Paul E. McKenney]

From: Frederic Weisbecker <fweisbec@gmail.com>

cpu_idle() is called on the boot CPU by the init code with
preemption disabled. But the cpu_idle() function in alpha
doesn't handle this when it calls schedule() directly.

Fix it by converting it into schedule_preempt_disabled().

Also disable preemption before calling cpu_idle() from
secondary CPU entry code to stay consistent with this
state.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Richard Henderson <rth@twiddle.net>
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: Matt Turner <mattst88@gmail.com>
Cc: alpha <linux-alpha@vger.kernel.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Michael Cree <mcree@orcon.net.nz>
---
 arch/alpha/kernel/process.c |    3 ++-
 arch/alpha/kernel/smp.c     |    1 +
 2 files changed, 3 insertions(+), 1 deletions(-)

diff --git a/arch/alpha/kernel/process.c b/arch/alpha/kernel/process.c
index 153d3fc..eac5e01 100644
--- a/arch/alpha/kernel/process.c
+++ b/arch/alpha/kernel/process.c
@@ -56,7 +56,8 @@ cpu_idle(void)
 
 		while (!need_resched())
 			cpu_relax();
-		schedule();
+
+		schedule_preempt_disabled();
 	}
 }
 
diff --git a/arch/alpha/kernel/smp.c b/arch/alpha/kernel/smp.c
index 35ddc02..a41ad90 100644
--- a/arch/alpha/kernel/smp.c
+++ b/arch/alpha/kernel/smp.c
@@ -166,6 +166,7 @@ smp_callin(void)
 	DBGS(("smp_callin: commencing CPU %d current %p active_mm %p\n",
 	      cpuid, current, current->active_mm));
 
+	preempt_disable();
 	/* Do nothing.  */
 	cpu_idle();
 }
-- 
1.7.8

[PATCH tip/core/rcu 16/26] alpha: Add missing RCU idle APIs on idle loop

[Paul E. McKenney]

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 Alpha's idle loop.

Reported-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Richard Henderson <rth@twiddle.net>
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: Matt Turner <mattst88@gmail.com>
Cc: alpha <linux-alpha@vger.kernel.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Michael Cree <mcree@orcon.net.nz>
Cc: 3.2.x.. <stable@vger.kernel.org>
---
 arch/alpha/kernel/process.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/arch/alpha/kernel/process.c b/arch/alpha/kernel/process.c
index eac5e01..eb9558c 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>
@@ -54,9 +55,11 @@ cpu_idle(void)
 		/* FIXME -- EV6 and LCA45 know how to power down
 		   the CPU.  */
 
+		rcu_idle_enter();
 		while (!need_resched())
 			cpu_relax();
 
+		rcu_idle_exit();
 		schedule_preempt_disabled();
 	}
 }
-- 
1.7.8

Re: [PATCH tip/core/rcu 15/26] alpha: Fix preemption handling in idle loop

[Josh Triplett]

On Thu, Aug 30, 2012 at 02:05:32PM -0700, Paul E. McKenney wrote:
> From: Frederic Weisbecker <fweisbec@gmail.com>
> 
> cpu_idle() is called on the boot CPU by the init code with
> preemption disabled. But the cpu_idle() function in alpha
> doesn't handle this when it calls schedule() directly.
> 
> Fix it by converting it into schedule_preempt_disabled().
> 
> Also disable preemption before calling cpu_idle() from
> secondary CPU entry code to stay consistent with this
> state.
> 
> Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
> Cc: Richard Henderson <rth@twiddle.net>
> Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
> Cc: Matt Turner <mattst88@gmail.com>
> Cc: alpha <linux-alpha@vger.kernel.org>
> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> Cc: Michael Cree <mcree@orcon.net.nz>

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

>  arch/alpha/kernel/process.c |    3 ++-
>  arch/alpha/kernel/smp.c     |    1 +
>  2 files changed, 3 insertions(+), 1 deletions(-)
> 
> diff --git a/arch/alpha/kernel/process.c b/arch/alpha/kernel/process.c
> index 153d3fc..eac5e01 100644
> --- a/arch/alpha/kernel/process.c
> +++ b/arch/alpha/kernel/process.c
> @@ -56,7 +56,8 @@ cpu_idle(void)
>  
>  		while (!need_resched())
>  			cpu_relax();
> -		schedule();
> +
> +		schedule_preempt_disabled();
>  	}
>  }
>  
> diff --git a/arch/alpha/kernel/smp.c b/arch/alpha/kernel/smp.c
> index 35ddc02..a41ad90 100644
> --- a/arch/alpha/kernel/smp.c
> +++ b/arch/alpha/kernel/smp.c
> @@ -166,6 +166,7 @@ smp_callin(void)
>  	DBGS(("smp_callin: commencing CPU %d current %p active_mm %p\n",
>  	      cpuid, current, current->active_mm));
>  
> +	preempt_disable();
>  	/* Do nothing.  */
>  	cpu_idle();
>  }
> -- 
> 1.7.8
> 

Re: [PATCH tip/core/rcu 16/26] alpha: Add missing RCU idle APIs on idle loop

[Josh Triplett]

On Thu, Aug 30, 2012 at 02:05:33PM -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 Alpha's idle loop.
> 
> Reported-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
> Cc: Richard Henderson <rth@twiddle.net>
> Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
> Cc: Matt Turner <mattst88@gmail.com>
> Cc: alpha <linux-alpha@vger.kernel.org>
> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> Cc: Michael Cree <mcree@orcon.net.nz>
> Cc: 3.2.x.. <stable@vger.kernel.org>

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

>  arch/alpha/kernel/process.c |    3 +++
>  1 files changed, 3 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/alpha/kernel/process.c b/arch/alpha/kernel/process.c
> index eac5e01..eb9558c 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>
> @@ -54,9 +55,11 @@ cpu_idle(void)
>  		/* FIXME -- EV6 and LCA45 know how to power down
>  		   the CPU.  */
>  
> +		rcu_idle_enter();
>  		while (!need_resched())
>  			cpu_relax();
>  
> +		rcu_idle_exit();
>  		schedule_preempt_disabled();
>  	}
>  }
> -- 
> 1.7.8
>