On Wed, Oct 31, 2012 at 07:23:03PM +0800, Shan Wei wrote:
> From: Shan Wei <davids...@tencent.com>
>
> smp_processor_id is defined as raw_smp_processor_id.
> replace per_cpu_ptr(p, raw_smp_processor_id()) is also ok.
>
> Signed-off-by: Shan Wei <davids...@tencent.com>
Hello, Shan Wei,
There are several definitions of this_cpu_ptr():
0 percpu.h 63 #define this_cpu_ptr(ptr) SHIFT_PERCPU_PTR(ptr, my_cpu_offset)
1 percpu.h 65 #define this_cpu_ptr(ptr) __this_cpu_ptr(ptr)
2 percpu.h 85 #define this_cpu_ptr(ptr) per_cpu_ptr(ptr, 0)
The first uses my_cpu_offset, which is further defined in two ways:
0 percpu.h 33 #define my_cpu_offset per_cpu_offset(smp_processor_id())
1 percpu.h 35 #define my_cpu_offset __my_cpu_offset
The first uses smp_processor_id(), which will complain if
force_quiescent_state() is called with preemption disabled, which it
sometimes is.
So what am I missing here?
Thanx, Paul
> ---
> kernel/rcutree.c | 2 +-
> 1 files changed, 1 insertions(+), 1 deletions(-)
>
> diff --git a/kernel/rcutree.c b/kernel/rcutree.c
> index 74df86b..3a21fcf 100644
> --- a/kernel/rcutree.c
> +++ b/kernel/rcutree.c
> @@ -1960,7 +1960,7 @@ static void force_quiescent_state(struct rcu_state *rsp)
> struct rcu_node *rnp_old = NULL;
>
> /* Funnel through hierarchy to reduce memory contention. */
> - rnp = per_cpu_ptr(rsp->rda, raw_smp_processor_id())->mynode;
> + rnp = this_cpu_ptr(rsp->rda)->mynode;
> for (; rnp != NULL; rnp = rnp->parent) {
> ret = (ACCESS_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) ||
> !raw_spin_trylock(&rnp->fqslock);
> --
> 1.7.1
>
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