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rcu: Abstract funnel locking from synchronize_sched_expedited() 

This commit abstracts funnel locking from synchronize_sched_expedited()
so that it may be used by synchronize_rcu_expedited().

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit is contained in:
Paul E. McKenney 2015-06-25 16:30:54 -07:00
parent 543c6158f6
commit b09e5f8601
1 changed files with 47 additions and 33 deletions
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80
kernel/rcu/tree.c
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@ -3309,16 +3309,6 @@ static bool rcu_exp_gp_seq_done(struct rcu_state *rsp, unsigned long s)
return rcu_seq_done(&rsp->expedited_sequence, s);
}
static int synchronize_sched_expedited_cpu_stop(void *data)
{
struct rcu_state *rsp = data;
/* We are here: If we are last, do the wakeup. */
if (atomic_dec_and_test(&rsp->expedited_need_qs))
wake_up(&rsp->expedited_wq);
return 0;
}
/* Common code for synchronize_sched_expedited() work-done checking. */
static bool sync_sched_exp_wd(struct rcu_state *rsp, struct rcu_node *rnp,
atomic_long_t *stat, unsigned long s)
@ -3335,6 +3325,48 @@ static bool sync_sched_exp_wd(struct rcu_state *rsp, struct rcu_node *rnp,
return false;
}
/*
* Funnel-lock acquisition for expedited grace periods. Returns a
* pointer to the root rcu_node structure, or NULL if some other
* task did the expedited grace period for us.
*/
static struct rcu_node *exp_funnel_lock(struct rcu_state *rsp, unsigned long s)
{
struct rcu_node *rnp0;
struct rcu_node *rnp1 = NULL;
/*
* Each pass through the following loop works its way
* up the rcu_node tree, returning if others have done the
* work or otherwise falls through holding the root rnp's
* ->exp_funnel_mutex. The mapping from CPU to rcu_node structure
* can be inexact, as it is just promoting locality and is not
* strictly needed for correctness.
*/
rnp0 = per_cpu_ptr(rsp->rda, raw_smp_processor_id())->mynode;
for (; rnp0 != NULL; rnp0 = rnp0->parent) {
if (sync_sched_exp_wd(rsp, rnp1, &rsp->expedited_workdone1, s))
return NULL;
mutex_lock(&rnp0->exp_funnel_mutex);
if (rnp1)
mutex_unlock(&rnp1->exp_funnel_mutex);
rnp1 = rnp0;
}
if (sync_sched_exp_wd(rsp, rnp1, &rsp->expedited_workdone2, s))
return NULL;
return rnp1;
}
static int synchronize_sched_expedited_cpu_stop(void *data)
{
struct rcu_state *rsp = data;
/* We are here: If we are last, do the wakeup. */
if (atomic_dec_and_test(&rsp->expedited_need_qs))
wake_up(&rsp->expedited_wq);
return 0;
}
/**
* synchronize_sched_expedited - Brute-force RCU-sched grace period
*
@ -3355,8 +3387,7 @@ void synchronize_sched_expedited(void)
{
int cpu;
long s;
struct rcu_node *rnp0;
struct rcu_node *rnp1 = NULL;
struct rcu_node *rnp;
struct rcu_state *rsp = &rcu_sched_state;
/* Take a snapshot of the sequence number. */
@ -3370,26 +3401,9 @@ void synchronize_sched_expedited(void)
}
WARN_ON_ONCE(cpu_is_offline(raw_smp_processor_id()));
/*
* Each pass through the following loop works its way
* up the rcu_node tree, returning if others have done the
* work or otherwise falls through holding the root rnp's
* ->exp_funnel_mutex. The mapping from CPU to rcu_node structure
* can be inexact, as it is just promoting locality and is not
* strictly needed for correctness.
*/
rnp0 = per_cpu_ptr(rsp->rda, raw_smp_processor_id())->mynode;
for (; rnp0 != NULL; rnp0 = rnp0->parent) {
if (sync_sched_exp_wd(rsp, rnp1, &rsp->expedited_workdone1, s))
return;
mutex_lock(&rnp0->exp_funnel_mutex);
if (rnp1)
mutex_unlock(&rnp1->exp_funnel_mutex);
rnp1 = rnp0;
}
rnp0 = rnp1; /* rcu_get_root(rsp), AKA root rcu_node structure. */
if (sync_sched_exp_wd(rsp, rnp0, &rsp->expedited_workdone2, s))
return;
rnp = exp_funnel_lock(rsp, s);
if (rnp == NULL)
return; /* Someone else did our work for us. */
rcu_exp_gp_seq_start(rsp);
@ -3415,7 +3429,7 @@ void synchronize_sched_expedited(void)
!atomic_read(&rsp->expedited_need_qs));
rcu_exp_gp_seq_end(rsp);
mutex_unlock(&rnp0->exp_funnel_mutex);
mutex_unlock(&rnp->exp_funnel_mutex);
smp_mb(); /* ensure subsequent action seen after grace period. */
put_online_cpus();