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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2017-03-10 15:31:55 -0800
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2017-04-18 11:38:20 -0700
commitc2a8ec0778b2ca0d360ba9b5cac7fcd5ddfe798f (patch)
tree03f3c9bd515211b30d58cd2d998969e020395ed5 /kernel/rcu
parentc6e56f593ac2df436700527c3488d4ed224c3acf (diff)
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srcu: Move to state-based grace-period sequencing
The current SRCU grace-period processing might never reach the last portion of srcu_advance_batches(). This is OK given the current implementation, as the first portion, up to the try_check_zero() following the srcu_flip() is sufficient to drive grace periods forward. However, it has the unfortunate side-effect of making it impossible to determine when a given grace period has ended, and it will be necessary to efficiently trace ends of grace periods in order to efficiently handle per-CPU SRCU callback lists. This commit therefore adds states to the SRCU grace-period processing, so that the end of a given SRCU grace period is marked by the transition to the SRCU_STATE_DONE state. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Diffstat (limited to 'kernel/rcu')
-rw-r--r--kernel/rcu/srcu.c111
1 files changed, 61 insertions, 50 deletions
diff --git a/kernel/rcu/srcu.c b/kernel/rcu/srcu.c
index 821ecda873f2..70286f68f3a1 100644
--- a/kernel/rcu/srcu.c
+++ b/kernel/rcu/srcu.c
@@ -111,7 +111,7 @@ static int init_srcu_struct_fields(struct srcu_struct *sp)
{
sp->completed = 0;
spin_lock_init(&sp->queue_lock);
- sp->running = false;
+ sp->srcu_state = SRCU_STATE_IDLE;
rcu_batch_init(&sp->batch_queue);
rcu_batch_init(&sp->batch_check0);
rcu_batch_init(&sp->batch_check1);
@@ -270,7 +270,7 @@ void cleanup_srcu_struct(struct srcu_struct *sp)
if (WARN_ON(!rcu_all_batches_empty(sp)))
return; /* Leakage unless caller handles error. */
flush_delayed_work(&sp->work);
- if (WARN_ON(sp->running))
+ if (WARN_ON(READ_ONCE(sp->srcu_state) != SRCU_STATE_IDLE))
return; /* Caller forgot to stop doing call_srcu()? */
free_percpu(sp->per_cpu_ref);
sp->per_cpu_ref = NULL;
@@ -391,8 +391,8 @@ void call_srcu(struct srcu_struct *sp, struct rcu_head *head,
spin_lock_irqsave(&sp->queue_lock, flags);
smp_mb__after_unlock_lock(); /* Caller's prior accesses before GP. */
rcu_batch_queue(&sp->batch_queue, head);
- if (!sp->running) {
- sp->running = true;
+ if (READ_ONCE(sp->srcu_state) == SRCU_STATE_IDLE) {
+ WRITE_ONCE(sp->srcu_state, SRCU_STATE_SCAN1);
queue_delayed_work(system_power_efficient_wq, &sp->work, 0);
}
spin_unlock_irqrestore(&sp->queue_lock, flags);
@@ -424,9 +424,9 @@ static void __synchronize_srcu(struct srcu_struct *sp, int trycount)
head->func = wakeme_after_rcu;
spin_lock_irq(&sp->queue_lock);
smp_mb__after_unlock_lock(); /* Caller's prior accesses before GP. */
- if (!sp->running) {
+ if (READ_ONCE(sp->srcu_state) == SRCU_STATE_IDLE) {
/* steal the processing owner */
- sp->running = true;
+ WRITE_ONCE(sp->srcu_state, SRCU_STATE_SCAN1);
rcu_batch_queue(&sp->batch_check0, head);
spin_unlock_irq(&sp->queue_lock);
/* give the processing owner to work_struct */
@@ -548,7 +548,9 @@ static void srcu_collect_new(struct srcu_struct *sp)
*/
static void srcu_advance_batches(struct srcu_struct *sp, int trycount)
{
- int idx = 1 ^ (sp->completed & 1);
+ int idx;
+
+ WARN_ON_ONCE(sp->srcu_state == SRCU_STATE_IDLE);
/*
* Because readers might be delayed for an extended period after
@@ -558,48 +560,56 @@ static void srcu_advance_batches(struct srcu_struct *sp, int trycount)
* invoking a callback.
*/
- if (rcu_batch_empty(&sp->batch_check0) &&
- rcu_batch_empty(&sp->batch_check1))
- return; /* no callbacks need to be advanced */
-
- if (!try_check_zero(sp, idx, trycount))
- return; /* failed to advance, will try after SRCU_INTERVAL */
-
- /*
- * The callbacks in ->batch_check1 have already done with their
- * first zero check and flip back when they were enqueued on
- * ->batch_check0 in a previous invocation of srcu_advance_batches().
- * (Presumably try_check_zero() returned false during that
- * invocation, leaving the callbacks stranded on ->batch_check1.)
- * They are therefore ready to invoke, so move them to ->batch_done.
- */
- rcu_batch_move(&sp->batch_done, &sp->batch_check1);
-
- if (rcu_batch_empty(&sp->batch_check0))
- return; /* no callbacks need to be advanced */
- srcu_flip(sp);
-
- /*
- * The callbacks in ->batch_check0 just finished their
- * first check zero and flip, so move them to ->batch_check1
- * for future checking on the other idx.
- */
- rcu_batch_move(&sp->batch_check1, &sp->batch_check0);
-
- /*
- * SRCU read-side critical sections are normally short, so check
- * at least twice in quick succession after a flip.
- */
- trycount = trycount < 2 ? 2 : trycount;
- if (!try_check_zero(sp, idx^1, trycount))
- return; /* failed to advance, will try after SRCU_INTERVAL */
+ if (sp->srcu_state == SRCU_STATE_DONE)
+ WRITE_ONCE(sp->srcu_state, SRCU_STATE_SCAN1);
+
+ if (sp->srcu_state == SRCU_STATE_SCAN1) {
+ idx = 1 ^ (sp->completed & 1);
+ if (!try_check_zero(sp, idx, trycount))
+ return; /* readers present, retry after SRCU_INTERVAL */
+
+ /*
+ * The callbacks in ->batch_check1 have already done
+ * with their first zero check and flip back when they were
+ * enqueued on ->batch_check0 in a previous invocation of
+ * srcu_advance_batches(). (Presumably try_check_zero()
+ * returned false during that invocation, leaving the
+ * callbacks stranded on ->batch_check1.) They are therefore
+ * ready to invoke, so move them to ->batch_done.
+ */
+ rcu_batch_move(&sp->batch_done, &sp->batch_check1);
+ srcu_flip(sp);
+
+ /*
+ * The callbacks in ->batch_check0 just finished their
+ * first check zero and flip, so move them to ->batch_check1
+ * for future checking on the other idx.
+ */
+ rcu_batch_move(&sp->batch_check1, &sp->batch_check0);
+
+ WRITE_ONCE(sp->srcu_state, SRCU_STATE_SCAN2);
+ }
- /*
- * The callbacks in ->batch_check1 have now waited for all
- * pre-existing readers using both idx values. They are therefore
- * ready to invoke, so move them to ->batch_done.
- */
- rcu_batch_move(&sp->batch_done, &sp->batch_check1);
+ if (sp->srcu_state == SRCU_STATE_SCAN2) {
+
+ /*
+ * SRCU read-side critical sections are normally short,
+ * so check at least twice in quick succession after a flip.
+ */
+ idx = 1 ^ (sp->completed & 1);
+ trycount = trycount < 2 ? 2 : trycount;
+ if (!try_check_zero(sp, idx, trycount))
+ return; /* readers present, retry after SRCU_INTERVAL */
+
+ /*
+ * The callbacks in ->batch_check1 have now waited for
+ * all pre-existing readers using both idx values. They are
+ * therefore ready to invoke, so move them to ->batch_done.
+ */
+ rcu_batch_move(&sp->batch_done, &sp->batch_check1);
+
+ WRITE_ONCE(sp->srcu_state, SRCU_STATE_DONE);
+ }
}
/*
@@ -633,8 +643,9 @@ static void srcu_reschedule(struct srcu_struct *sp, unsigned long delay)
if (rcu_all_batches_empty(sp)) {
spin_lock_irq(&sp->queue_lock);
- if (rcu_all_batches_empty(sp)) {
- sp->running = false;
+ if (rcu_all_batches_empty(sp) &&
+ READ_ONCE(sp->srcu_state) == SRCU_STATE_DONE) {
+ WRITE_ONCE(sp->srcu_state, SRCU_STATE_IDLE);
pending = false;
}
spin_unlock_irq(&sp->queue_lock);