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rcu: Break up rcu_gp_kthread() into subfunctions
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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>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
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Paul E. McKenney committed Sep 23, 2012
1 parent c856baf commit 7fdefc1
Showing 1 changed file with 135 additions and 115 deletions.
250 changes: 135 additions & 115 deletions kernel/rcutree.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1028,95 +1028,159 @@ 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 __noreturn rcu_gp_kthread(void *arg)
static int rcu_gp_init(struct rcu_state *rsp)
{
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_irq(&rnp->lock);
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_irq(&rnp->lock);
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_irq(&rnp->lock);
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_irq(&rnp->lock);

/* 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
* will 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_irq(&rnp->lock);
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_irq(&rnp->lock);
cond_resched();
}

if (rcu_gp_in_progress(rsp)) {
/*
* A grace period is already in progress, so
* don't start another one.
*/
raw_spin_unlock_irq(&rnp->lock);
cond_resched();
continue;
}
rnp = rcu_get_root(rsp);
raw_spin_lock_irq(&rnp->lock);
/* force_quiescent_state() now OK. */
rsp->fqs_state = RCU_SIGNAL_INIT;
raw_spin_unlock_irq(&rnp->lock);
put_online_cpus();
return 1;
}

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_irq(&rnp->lock);
cond_resched();
continue;
}
/*
* Clean up after the old grace period.
*/
static int rcu_gp_cleanup(struct rcu_state *rsp)
{
unsigned long gp_duration;
struct rcu_data *rdp;
struct rcu_node *rnp = rcu_get_root(rsp);

/* 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_irq(&rnp->lock);
raw_spin_lock_irq(&rnp->lock);
gp_duration = jiffies - rsp->gp_start;
if (gp_duration > rsp->gp_max)
rsp->gp_max = gp_duration;

/* Exclude any concurrent CPU-hotplug operations. */
get_online_cpus();
/*
* 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_irq(&rnp->lock);

/*
* 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.
* 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_irq(&rnp->lock);
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_irq(&rnp->lock);
cond_resched();
}

rnp = rcu_get_root(rsp);
raw_spin_lock_irq(&rnp->lock);
/* force_quiescent_state() now OK. */
rsp->fqs_state = RCU_SIGNAL_INIT;
raw_spin_unlock_irq(&rnp->lock);
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;
if (cpu_needs_another_gp(rsp, rdp))
rsp->gp_flags = 1;
raw_spin_unlock_irq(&rnp->lock);
return 1;
}

/*
* Body of kthread that handles grace periods.
*/
static int __noreturn 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);
Expand All @@ -1125,56 +1189,12 @@ static int __noreturn rcu_gp_kthread(void *arg)
!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_irq(&rnp->lock);
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_irq(&rnp->lock);

/*
* 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_irq(&rnp->lock);
rnp->completed = rsp->gpnum;
raw_spin_unlock_irq(&rnp->lock);
cond_resched();
}
rnp = rcu_get_root(rsp);
raw_spin_lock_irq(&rnp->lock);
}

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_irq(&rnp->lock);
}
}

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