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Subject[PATCH tip/core/rcu 06/23] rcu: Break up rcu_gp_kthread() into subfunctions
Date
From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>

Then rcu_gp_kthread() function is too large and furthermore needs to
have the force_quiescent_state() code pulled in. This commit therefore
breaks up rcu_gp_kthread() into rcu_gp_init() and rcu_gp_cleanup().

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
kernel/rcutree.c | 260 +++++++++++++++++++++++++++++-------------------------
1 files changed, 138 insertions(+), 122 deletions(-)
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 84a6f55..c2c036f 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -1040,160 +1040,176 @@ rcu_start_gp_per_cpu(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_dat
}

/*
- * Body of kthread that handles grace periods.
+ * Initialize a new grace period.
*/
-static int rcu_gp_kthread(void *arg)
+static int rcu_gp_init(struct rcu_state *rsp)
{
unsigned long flags;
- unsigned long gp_duration;
struct rcu_data *rdp;
- struct rcu_node *rnp;
- struct rcu_state *rsp = arg;
+ struct rcu_node *rnp = rcu_get_root(rsp);

- for (;;) {
+ raw_spin_lock_irqsave(&rnp->lock, flags);
+ rsp->gp_flags = 0;

- /* Handle grace-period start. */
- rnp = rcu_get_root(rsp);
- for (;;) {
- wait_event_interruptible(rsp->gp_wq, rsp->gp_flags);
- if (rsp->gp_flags)
- break;
- flush_signals(current);
- }
+ if (rcu_gp_in_progress(rsp)) {
+ /* Grace period already in progress, don't start another. */
+ raw_spin_unlock_irqrestore(&rnp->lock, flags);
+ return 0;
+ }
+
+ if (rsp->fqs_active) {
+ /*
+ * We need a grace period, but force_quiescent_state()
+ * is running. Tell it to start one on our behalf.
+ */
+ rsp->fqs_need_gp = 1;
+ raw_spin_unlock_irqrestore(&rnp->lock, flags);
+ return 0;
+ }
+
+ /* Advance to a new grace period and initialize state. */
+ rsp->gpnum++;
+ trace_rcu_grace_period(rsp->name, rsp->gpnum, "start");
+ WARN_ON_ONCE(rsp->fqs_state == RCU_GP_INIT);
+ rsp->fqs_state = RCU_GP_INIT; /* Stop force_quiescent_state. */
+ rsp->jiffies_force_qs = jiffies + RCU_JIFFIES_TILL_FORCE_QS;
+ record_gp_stall_check_time(rsp);
+ raw_spin_unlock_irqrestore(&rnp->lock, flags);
+
+ /* Exclude any concurrent CPU-hotplug operations. */
+ get_online_cpus();
+
+ /*
+ * Set the quiescent-state-needed bits in all the rcu_node
+ * structures for all currently online CPUs in breadth-first order,
+ * starting from the root rcu_node structure, relying on the layout
+ * of the tree within the rsp->node[] array. Note that other CPUs
+ * access only the leaves of the hierarchy, thus seeing that no
+ * grace period is in progress, at least until the corresponding
+ * leaf node has been initialized. In addition, we have excluded
+ * CPU-hotplug operations.
+ *
+ * The grace period cannot complete until the initialization
+ * process finishes, because this kthread handles both.
+ */
+ rcu_for_each_node_breadth_first(rsp, rnp) {
raw_spin_lock_irqsave(&rnp->lock, flags);
- rsp->gp_flags = 0;
rdp = this_cpu_ptr(rsp->rda);
+ rcu_preempt_check_blocked_tasks(rnp);
+ rnp->qsmask = rnp->qsmaskinit;
+ rnp->gpnum = rsp->gpnum;
+ rnp->completed = rsp->completed;
+ if (rnp == rdp->mynode)
+ rcu_start_gp_per_cpu(rsp, rnp, rdp);
+ rcu_preempt_boost_start_gp(rnp);
+ trace_rcu_grace_period_init(rsp->name, rnp->gpnum,
+ rnp->level, rnp->grplo,
+ rnp->grphi, rnp->qsmask);
+ raw_spin_unlock_irqrestore(&rnp->lock, flags);
+ cond_resched();
+ }

- if (rcu_gp_in_progress(rsp)) {
- /*
- * A grace period is already in progress, so
- * don't start another one.
- */
- raw_spin_unlock_irqrestore(&rnp->lock, flags);
- cond_resched();
- continue;
- }
+ rnp = rcu_get_root(rsp);
+ raw_spin_lock_irqsave(&rnp->lock, flags);
+ /* force_quiescent_state() now OK. */
+ rsp->fqs_state = RCU_SIGNAL_INIT;
+ raw_spin_unlock_irqrestore(&rnp->lock, flags);
+ put_online_cpus();

- if (rsp->fqs_active) {
- /*
- * We need a grace period, but force_quiescent_state()
- * is running. Tell it to start one on our behalf.
- */
- rsp->fqs_need_gp = 1;
- raw_spin_unlock_irqrestore(&rnp->lock, flags);
- cond_resched();
- continue;
- }
+ return 1;
+}

- /* Advance to a new grace period and initialize state. */
- rsp->gpnum++;
- trace_rcu_grace_period(rsp->name, rsp->gpnum, "start");
- WARN_ON_ONCE(rsp->fqs_state == RCU_GP_INIT);
- rsp->fqs_state = RCU_GP_INIT; /* Stop force_quiescent_state. */
- rsp->jiffies_force_qs = jiffies + RCU_JIFFIES_TILL_FORCE_QS;
- record_gp_stall_check_time(rsp);
- raw_spin_unlock_irqrestore(&rnp->lock, flags);
+/*
+ * Clean up after the old grace period.
+ */
+static int rcu_gp_cleanup(struct rcu_state *rsp)
+{
+ unsigned long flags;
+ unsigned long gp_duration;
+ struct rcu_data *rdp;
+ struct rcu_node *rnp = rcu_get_root(rsp);

- /* Exclude any concurrent CPU-hotplug operations. */
- get_online_cpus();
+ raw_spin_lock_irqsave(&rnp->lock, flags);
+ gp_duration = jiffies - rsp->gp_start;
+ if (gp_duration > rsp->gp_max)
+ rsp->gp_max = gp_duration;
+
+ /*
+ * We know the grace period is complete, but to everyone else
+ * it appears to still be ongoing. But it is also the case
+ * that to everyone else it looks like there is nothing that
+ * they can do to advance the grace period. It is therefore
+ * safe for us to drop the lock in order to mark the grace
+ * period as completed in all of the rcu_node structures.
+ *
+ * But if this CPU needs another grace period, it will take
+ * care of this while initializing the next grace period.
+ * We use RCU_WAIT_TAIL instead of the usual RCU_DONE_TAIL
+ * because the callbacks have not yet been advanced: Those
+ * callbacks are waiting on the grace period that just now
+ * completed.
+ */
+ rdp = this_cpu_ptr(rsp->rda);
+ if (*rdp->nxttail[RCU_WAIT_TAIL] == NULL) {
+ raw_spin_unlock_irqrestore(&rnp->lock, flags);

/*
- * Set the quiescent-state-needed bits in all the rcu_node
- * structures for all currently online CPUs in breadth-first
- * order, starting from the root rcu_node structure.
- * This operation relies on the layout of the hierarchy
- * within the rsp->node[] array. Note that other CPUs will
- * access only the leaves of the hierarchy, which still
- * indicate that no grace period is in progress, at least
- * until the corresponding leaf node has been initialized.
- * In addition, we have excluded CPU-hotplug operations.
- *
- * Note that the grace period cannot complete until
- * we finish the initialization process, as there will
- * be at least one qsmask bit set in the root node until
- * that time, namely the one corresponding to this CPU,
- * due to the fact that we have irqs disabled.
+ * Propagate new ->completed value to rcu_node
+ * structures so that other CPUs don't have to
+ * wait until the start of the next grace period
+ * to process their callbacks.
*/
rcu_for_each_node_breadth_first(rsp, rnp) {
raw_spin_lock_irqsave(&rnp->lock, flags);
- rcu_preempt_check_blocked_tasks(rnp);
- rnp->qsmask = rnp->qsmaskinit;
- rnp->gpnum = rsp->gpnum;
- rnp->completed = rsp->completed;
- if (rnp == rdp->mynode)
- rcu_start_gp_per_cpu(rsp, rnp, rdp);
- rcu_preempt_boost_start_gp(rnp);
- trace_rcu_grace_period_init(rsp->name, rnp->gpnum,
- rnp->level, rnp->grplo,
- rnp->grphi, rnp->qsmask);
+ rnp->completed = rsp->gpnum;
raw_spin_unlock_irqrestore(&rnp->lock, flags);
cond_resched();
}
-
rnp = rcu_get_root(rsp);
raw_spin_lock_irqsave(&rnp->lock, flags);
- /* force_quiescent_state() now OK. */
- rsp->fqs_state = RCU_SIGNAL_INIT;
- raw_spin_unlock_irqrestore(&rnp->lock, flags);
- put_online_cpus();
+ }
+
+ rsp->completed = rsp->gpnum; /* Declare grace period done. */
+ trace_rcu_grace_period(rsp->name, rsp->completed, "end");
+ rsp->fqs_state = RCU_GP_IDLE;
+ rdp = this_cpu_ptr(rsp->rda);
+ if (cpu_needs_another_gp(rsp, rdp))
+ rsp->gp_flags = 1;
+ raw_spin_unlock_irqrestore(&rnp->lock, flags);
+ return 1;
+}
+
+/*
+ * Body of kthread that handles grace periods.
+ */
+static int rcu_gp_kthread(void *arg)
+{
+ struct rcu_state *rsp = arg;
+ struct rcu_node *rnp = rcu_get_root(rsp);
+
+ for (;;) {
+
+ /* Handle grace-period start. */
+ for (;;) {
+ wait_event_interruptible(rsp->gp_wq, rsp->gp_flags);
+ if (rsp->gp_flags && rcu_gp_init(rsp))
+ break;
+ cond_resched();
+ flush_signals(current);
+ }

/* Handle grace-period end. */
- rnp = rcu_get_root(rsp);
for (;;) {
wait_event_interruptible(rsp->gp_wq,
!ACCESS_ONCE(rnp->qsmask) &&
!rcu_preempt_blocked_readers_cgp(rnp));
if (!ACCESS_ONCE(rnp->qsmask) &&
- !rcu_preempt_blocked_readers_cgp(rnp))
+ !rcu_preempt_blocked_readers_cgp(rnp) &&
+ rcu_gp_cleanup(rsp))
break;
+ cond_resched();
flush_signals(current);
}
-
- raw_spin_lock_irqsave(&rnp->lock, flags);
- gp_duration = jiffies - rsp->gp_start;
- if (gp_duration > rsp->gp_max)
- rsp->gp_max = gp_duration;
-
- /*
- * We know the grace period is complete, but to everyone else
- * it appears to still be ongoing. But it is also the case
- * that to everyone else it looks like there is nothing that
- * they can do to advance the grace period. It is therefore
- * safe for us to drop the lock in order to mark the grace
- * period as completed in all of the rcu_node structures.
- *
- * But if this CPU needs another grace period, it will take
- * care of this while initializing the next grace period.
- * We use RCU_WAIT_TAIL instead of the usual RCU_DONE_TAIL
- * because the callbacks have not yet been advanced: Those
- * callbacks are waiting on the grace period that just now
- * completed.
- */
- if (*rdp->nxttail[RCU_WAIT_TAIL] == NULL) {
- raw_spin_unlock_irqrestore(&rnp->lock, flags);
-
- /*
- * Propagate new ->completed value to rcu_node
- * structures so that other CPUs don't have to
- * wait until the start of the next grace period
- * to process their callbacks.
- */
- rcu_for_each_node_breadth_first(rsp, rnp) {
- raw_spin_lock_irqsave(&rnp->lock, flags);
- rnp->completed = rsp->gpnum;
- raw_spin_unlock_irqrestore(&rnp->lock, flags);
- cond_resched();
- }
- rnp = rcu_get_root(rsp);
- raw_spin_lock_irqsave(&rnp->lock, flags);
- }
-
- rsp->completed = rsp->gpnum; /* Declare grace period done. */
- trace_rcu_grace_period(rsp->name, rsp->completed, "end");
- rsp->fqs_state = RCU_GP_IDLE;
- if (cpu_needs_another_gp(rsp, rdp))
- rsp->gp_flags = 1;
- raw_spin_unlock_irqrestore(&rnp->lock, flags);
}
return 0;
}
--
1.7.8


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