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rcu: Add expedited grace-period support for preemptible RCU

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Implement an synchronize_rcu_expedited() for preemptible RCU
that actually is expedited.  This uses
synchronize_sched_expedited() to force all threads currently
running in a preemptible-RCU read-side critical section onto the
appropriate ->blocked_tasks[] list, then takes a snapshot of all
of these lists and waits for them to drain.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference: <1259784616158-git-send-email->
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Paul E. McKenney
2009-12-02 12:10:15 -08:00
committed by Ingo Molnar
parent cf244dc01b
commit d9a3da0699
5 changed files with 260 additions and 27 deletions
Download Patch File Download Diff File Expand all files Collapse all files

198
kernel/rcutree_plugin.h
View File

@@ -24,12 +24,15 @@
* Paul E. McKenney <paulmck@linux.vnet.ibm.com>
*/
#include <linux/delay.h>
#ifdef CONFIG_TREE_PREEMPT_RCU
struct rcu_state rcu_preempt_state = RCU_STATE_INITIALIZER(rcu_preempt_state);
DEFINE_PER_CPU(struct rcu_data, rcu_preempt_data);
static int rcu_preempted_readers_exp(struct rcu_node *rnp);
/*
* Tell them what RCU they are running.
*/
@@ -157,7 +160,10 @@ EXPORT_SYMBOL_GPL(__rcu_read_lock);
*/
static int rcu_preempted_readers(struct rcu_node *rnp)
{
return !list_empty(&rnp->blocked_tasks[rnp->gpnum & 0x1]);
int phase = rnp->gpnum & 0x1;
return !list_empty(&rnp->blocked_tasks[phase]) ||
!list_empty(&rnp->blocked_tasks[phase + 2]);
}
/*
@@ -204,6 +210,7 @@ static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)
static void rcu_read_unlock_special(struct task_struct *t)
{
int empty;
int empty_exp;
unsigned long flags;
struct rcu_node *rnp;
int special;
@@ -247,6 +254,8 @@ static void rcu_read_unlock_special(struct task_struct *t)
spin_unlock(&rnp->lock); /* irqs remain disabled. */
}
empty = !rcu_preempted_readers(rnp);
empty_exp = !rcu_preempted_readers_exp(rnp);
smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */
list_del_init(&t->rcu_node_entry);
t->rcu_blocked_node = NULL;
@@ -259,6 +268,13 @@ static void rcu_read_unlock_special(struct task_struct *t)
spin_unlock_irqrestore(&rnp->lock, flags);
else
rcu_report_unblock_qs_rnp(rnp, flags);
/*
* If this was the last task on the expedited lists,
* then we need to report up the rcu_node hierarchy.
*/
if (!empty_exp && !rcu_preempted_readers_exp(rnp))
rcu_report_exp_rnp(&rcu_preempt_state, rnp);
} else {
local_irq_restore(flags);
}
@@ -343,7 +359,7 @@ static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
int i;
struct list_head *lp;
struct list_head *lp_root;
int retval;
int retval = 0;
struct rcu_node *rnp_root = rcu_get_root(rsp);
struct task_struct *tp;
@@ -353,7 +369,9 @@ static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
}
WARN_ON_ONCE(rnp != rdp->mynode &&
(!list_empty(&rnp->blocked_tasks[0]) ||
!list_empty(&rnp->blocked_tasks[1])));
!list_empty(&rnp->blocked_tasks[1]) ||
!list_empty(&rnp->blocked_tasks[2]) ||
!list_empty(&rnp->blocked_tasks[3])));
/*
* Move tasks up to root rcu_node. Rely on the fact that the
@@ -361,8 +379,11 @@ static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
* rcu_nodes in terms of gp_num value. This fact allows us to
* move the blocked_tasks[] array directly, element by element.
*/
retval = rcu_preempted_readers(rnp);
for (i = 0; i < 2; i++) {
if (rcu_preempted_readers(rnp))
retval |= RCU_OFL_TASKS_NORM_GP;
if (rcu_preempted_readers_exp(rnp))
retval |= RCU_OFL_TASKS_EXP_GP;
for (i = 0; i < 4; i++) {
lp = &rnp->blocked_tasks[i];
lp_root = &rnp_root->blocked_tasks[i];
while (!list_empty(lp)) {
@@ -449,14 +470,159 @@ void synchronize_rcu(void)
}
EXPORT_SYMBOL_GPL(synchronize_rcu);
static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq);
static long sync_rcu_preempt_exp_count;
static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex);
/*
* Wait for an rcu-preempt grace period. We are supposed to expedite the
* grace period, but this is the crude slow compatability hack, so just
* invoke synchronize_rcu().
* Return non-zero if there are any tasks in RCU read-side critical
* sections blocking the current preemptible-RCU expedited grace period.
* If there is no preemptible-RCU expedited grace period currently in
* progress, returns zero unconditionally.
*/
static int rcu_preempted_readers_exp(struct rcu_node *rnp)
{
return !list_empty(&rnp->blocked_tasks[2]) ||
!list_empty(&rnp->blocked_tasks[3]);
}
/*
* return non-zero if there is no RCU expedited grace period in progress
* for the specified rcu_node structure, in other words, if all CPUs and
* tasks covered by the specified rcu_node structure have done their bit
* for the current expedited grace period. Works only for preemptible
* RCU -- other RCU implementation use other means.
*
* Caller must hold sync_rcu_preempt_exp_mutex.
*/
static int sync_rcu_preempt_exp_done(struct rcu_node *rnp)
{
return !rcu_preempted_readers_exp(rnp) &&
ACCESS_ONCE(rnp->expmask) == 0;
}
/*
* Report the exit from RCU read-side critical section for the last task
* that queued itself during or before the current expedited preemptible-RCU
* grace period. This event is reported either to the rcu_node structure on
* which the task was queued or to one of that rcu_node structure's ancestors,
* recursively up the tree. (Calm down, calm down, we do the recursion
* iteratively!)
*
* Caller must hold sync_rcu_preempt_exp_mutex.
*/
static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp)
{
unsigned long flags;
unsigned long mask;
spin_lock_irqsave(&rnp->lock, flags);
for (;;) {
if (!sync_rcu_preempt_exp_done(rnp))
break;
if (rnp->parent == NULL) {
wake_up(&sync_rcu_preempt_exp_wq);
break;
}
mask = rnp->grpmask;
spin_unlock(&rnp->lock); /* irqs remain disabled */
rnp = rnp->parent;
spin_lock(&rnp->lock); /* irqs already disabled */
rnp->expmask &= ~mask;
}
spin_unlock_irqrestore(&rnp->lock, flags);
}
/*
* Snapshot the tasks blocking the newly started preemptible-RCU expedited
* grace period for the specified rcu_node structure. If there are no such
* tasks, report it up the rcu_node hierarchy.
*
* Caller must hold sync_rcu_preempt_exp_mutex and rsp->onofflock.
*/
static void
sync_rcu_preempt_exp_init(struct rcu_state *rsp, struct rcu_node *rnp)
{
int must_wait;
spin_lock(&rnp->lock); /* irqs already disabled */
list_splice_init(&rnp->blocked_tasks[0], &rnp->blocked_tasks[2]);
list_splice_init(&rnp->blocked_tasks[1], &rnp->blocked_tasks[3]);
must_wait = rcu_preempted_readers_exp(rnp);
spin_unlock(&rnp->lock); /* irqs remain disabled */
if (!must_wait)
rcu_report_exp_rnp(rsp, rnp);
}
/*
* Wait for an rcu-preempt grace period, but expedite it. The basic idea
* is to invoke synchronize_sched_expedited() to push all the tasks to
* the ->blocked_tasks[] lists, move all entries from the first set of
* ->blocked_tasks[] lists to the second set, and finally wait for this
* second set to drain.
*/
void synchronize_rcu_expedited(void)
{
synchronize_rcu();
unsigned long flags;
struct rcu_node *rnp;
struct rcu_state *rsp = &rcu_preempt_state;
long snap;
int trycount = 0;
smp_mb(); /* Caller's modifications seen first by other CPUs. */
snap = ACCESS_ONCE(sync_rcu_preempt_exp_count) + 1;
smp_mb(); /* Above access cannot bleed into critical section. */
/*
* Acquire lock, falling back to synchronize_rcu() if too many
* lock-acquisition failures. Of course, if someone does the
* expedited grace period for us, just leave.
*/
while (!mutex_trylock(&sync_rcu_preempt_exp_mutex)) {
if (trycount++ < 10)
udelay(trycount * num_online_cpus());
else {
synchronize_rcu();
return;
}
if ((ACCESS_ONCE(sync_rcu_preempt_exp_count) - snap) > 0)
goto mb_ret; /* Others did our work for us. */
}
if ((ACCESS_ONCE(sync_rcu_preempt_exp_count) - snap) > 0)
goto unlock_mb_ret; /* Others did our work for us. */
/* force all RCU readers onto blocked_tasks[]. */
synchronize_sched_expedited();
spin_lock_irqsave(&rsp->onofflock, flags);
/* Initialize ->expmask for all non-leaf rcu_node structures. */
rcu_for_each_nonleaf_node_breadth_first(rsp, rnp) {
spin_lock(&rnp->lock); /* irqs already disabled. */
rnp->expmask = rnp->qsmaskinit;
spin_unlock(&rnp->lock); /* irqs remain disabled. */
}
/* Snapshot current state of ->blocked_tasks[] lists. */
rcu_for_each_leaf_node(rsp, rnp)
sync_rcu_preempt_exp_init(rsp, rnp);
if (NUM_RCU_NODES > 1)
sync_rcu_preempt_exp_init(rsp, rcu_get_root(rsp));
spin_unlock_irqrestore(&rsp->onofflock, flags);
/* Wait for snapshotted ->blocked_tasks[] lists to drain. */
rnp = rcu_get_root(rsp);
wait_event(sync_rcu_preempt_exp_wq,
sync_rcu_preempt_exp_done(rnp));
/* Clean up and exit. */
smp_mb(); /* ensure expedited GP seen before counter increment. */
ACCESS_ONCE(sync_rcu_preempt_exp_count)++;
unlock_mb_ret:
mutex_unlock(&sync_rcu_preempt_exp_mutex);
mb_ret:
smp_mb(); /* ensure subsequent action seen after grace period. */
}
EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
@@ -655,6 +821,20 @@ void synchronize_rcu_expedited(void)
}
EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
#ifdef CONFIG_HOTPLUG_CPU
/*
* Because preemptable RCU does not exist, there is never any need to
* report on tasks preempted in RCU read-side critical sections during
* expedited RCU grace periods.
*/
static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp)
{
return;
}
#endif /* #ifdef CONFIG_HOTPLUG_CPU */
/*
* Because preemptable RCU does not exist, it never has any work to do.
*/