Re: [PATCH tip/core/rcu 08/15] rcu: Move rcu_barrier_mutex torcu_state structure

From: Josh Triplett
Date: Fri Jun 15 2012 - 18:55:26 EST


On Fri, Jun 15, 2012 at 02:06:03PM -0700, Paul E. McKenney wrote:
> From: "Paul E. McKenney" <paul.mckenney@xxxxxxxxxx>
>
> In order to allow each RCU flavor to concurrently execute its
> rcu_barrier() function, it is necessary to move the relevant
> state to the rcu_state structure. This commit therefore moves the
> rcu_barrier_mutex global variable to a new ->barrier_mutex field
> in the rcu_state structure.
>
> Signed-off-by: Paul E. McKenney <paul.mckenney@xxxxxxxxxx>
> Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
> ---
> kernel/rcutree.c | 11 +++--------
> kernel/rcutree.h | 1 +
> 2 files changed, 4 insertions(+), 8 deletions(-)
>
> diff --git a/kernel/rcutree.c b/kernel/rcutree.c
> index a946437..93358d4 100644
> --- a/kernel/rcutree.c
> +++ b/kernel/rcutree.c
> @@ -71,9 +71,8 @@ static struct lock_class_key rcu_node_class[RCU_NUM_LVLS];
> .onofflock = __RAW_SPIN_LOCK_UNLOCKED(&sname##_state.onofflock), \
> .orphan_nxttail = &sname##_state.orphan_nxtlist, \
> .orphan_donetail = &sname##_state.orphan_donelist, \
> + .barrier_mutex = __MUTEX_INITIALIZER(sname##_state.barrier_mutex), \
> .fqslock = __RAW_SPIN_LOCK_UNLOCKED(&sname##_state.fqslock), \
> - .n_force_qs = 0, \
> - .n_force_qs_ngp = 0, \

The removal of these two fields seems unrelated to the rest of this
commit.

I assume you've removed them because the use of "static" makes
initializations to 0 unnecessary?

The rest of this commit seems fine to me.

> .name = #sname, \
> }
>
> @@ -155,10 +154,6 @@ static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp);
> unsigned long rcutorture_testseq;
> unsigned long rcutorture_vernum;
>
> -/* State information for rcu_barrier() and friends. */
> -
> -static DEFINE_MUTEX(rcu_barrier_mutex);
> -
> /*
> * Return true if an RCU grace period is in progress. The ACCESS_ONCE()s
> * permit this function to be invoked without holding the root rcu_node
> @@ -2300,7 +2295,7 @@ static void _rcu_barrier(struct rcu_state *rsp)
> init_rcu_head_on_stack(&rd.barrier_head);
>
> /* Take mutex to serialize concurrent rcu_barrier() requests. */
> - mutex_lock(&rcu_barrier_mutex);
> + mutex_lock(&rsp->barrier_mutex);
>
> smp_mb(); /* Prevent any prior operations from leaking in. */
>
> @@ -2377,7 +2372,7 @@ static void _rcu_barrier(struct rcu_state *rsp)
> wait_for_completion(&rsp->barrier_completion);
>
> /* Other rcu_barrier() invocations can now safely proceed. */
> - mutex_unlock(&rcu_barrier_mutex);
> + mutex_unlock(&rsp->barrier_mutex);
>
> destroy_rcu_head_on_stack(&rd.barrier_head);
> }
> diff --git a/kernel/rcutree.h b/kernel/rcutree.h
> index 56fb8d4..d9ac82f 100644
> --- a/kernel/rcutree.h
> +++ b/kernel/rcutree.h
> @@ -386,6 +386,7 @@ struct rcu_state {
> struct task_struct *rcu_barrier_in_progress;
> /* Task doing rcu_barrier(), */
> /* or NULL if no barrier. */
> + struct mutex barrier_mutex; /* Guards barrier fields. */
> atomic_t barrier_cpu_count; /* # CPUs waiting on. */
> struct completion barrier_completion; /* Wake at barrier end. */
> raw_spinlock_t fqslock; /* Only one task forcing */
> --
> 1.7.8
>
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