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Message-Id: <1484707528-2176-3-git-send-email-paulmck@linux.vnet.ibm.com>
Date: Tue, 17 Jan 2017 18:45:25 -0800
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To: linux-kernel@...r.kernel.org
Cc: mingo@...nel.org, jiangshanlai@...il.com, dipankar@...ibm.com,
akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
dvhart@...ux.intel.com, fweisbec@...il.com, oleg@...hat.com,
bobby.prani@...il.com,
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH v2 tip/core/rcu 3/6] rcu: Abstract dynticks extended quiescent state enter/exit operations
This commit is the third step towards full abstraction of all accesses
to the ->dynticks counter, implementing the previously open-coded atomic
add of 1 and entry checks in a new rcu_dynticks_eqs_enter() function, and
the same but with exit checks in a new rcu_dynticks_eqs_exit() function.
This abstraction will ease changes to the ->dynticks counter operation.
Note that this commit gets rid of the smp_mb__before_atomic() and the
smp_mb__after_atomic() calls that were previously present. The reason
that this is OK from a memory-ordering perspective is that the atomic
operation is now atomic_add_return(), which, as a value-returning atomic,
guarantees full ordering.
Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
kernel/rcu/tree.c | 88 +++++++++++++++++++++++++++++++++++++++----------------
1 file changed, 62 insertions(+), 26 deletions(-)
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 805d55ee0b2a..70b01e1983e6 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -282,6 +282,61 @@ static DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = {
};
/*
+ * Record entry into an extended quiescent state. This is only to be
+ * called when not already in an extended quiescent state.
+ */
+static void rcu_dynticks_eqs_enter(void)
+{
+ struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
+ int special;
+
+ /*
+ * CPUs seeing atomic_inc_return() must see prior RCU read-side
+ * critical sections, and we also must force ordering with the
+ * next idle sojourn.
+ */
+ special = atomic_inc_return(&rdtp->dynticks);
+ WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && special & 0x1);
+}
+
+/*
+ * Record exit from an extended quiescent state. This is only to be
+ * called from an extended quiescent state.
+ */
+static void rcu_dynticks_eqs_exit(void)
+{
+ struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
+ int special;
+
+ /*
+ * CPUs seeing atomic_inc_return() must see prior idle sojourns,
+ * and we also must force ordering with the next RCU read-side
+ * critical section.
+ */
+ special = atomic_inc_return(&rdtp->dynticks);
+ WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !(special & 0x1));
+}
+
+/*
+ * Reset the current CPU's ->dynticks counter to indicate that the
+ * newly onlined CPU is no longer in an extended quiescent state.
+ * This will either leave the counter unchanged, or increment it
+ * to the next non-quiescent value.
+ *
+ * The non-atomic test/increment sequence works because the upper bits
+ * of the ->dynticks counter are manipulated only by the corresponding CPU,
+ * or when the corresponding CPU is offline.
+ */
+static void rcu_dynticks_eqs_online(void)
+{
+ struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
+
+ if (atomic_read(&rdtp->dynticks) & 0x1)
+ return;
+ atomic_add(0x1, &rdtp->dynticks);
+}
+
+/*
* Snapshot the ->dynticks counter with full ordering so as to allow
* stable comparison of this counter with past and future snapshots.
*/
@@ -693,7 +748,7 @@ static void rcu_eqs_enter_common(long long oldval, bool user)
{
struct rcu_state *rsp;
struct rcu_data *rdp;
- struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
+ RCU_TRACE(struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks));
trace_rcu_dyntick(TPS("Start"), oldval, rdtp->dynticks_nesting);
if (IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
@@ -712,12 +767,7 @@ static void rcu_eqs_enter_common(long long oldval, bool user)
do_nocb_deferred_wakeup(rdp);
}
rcu_prepare_for_idle();
- /* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */
- smp_mb__before_atomic(); /* See above. */
- atomic_inc(&rdtp->dynticks);
- smp_mb__after_atomic(); /* Force ordering with next sojourn. */
- WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
- atomic_read(&rdtp->dynticks) & 0x1);
+ rcu_dynticks_eqs_enter();
rcu_dynticks_task_enter();
/*
@@ -846,15 +896,10 @@ void rcu_irq_exit_irqson(void)
*/
static void rcu_eqs_exit_common(long long oldval, int user)
{
- struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
+ RCU_TRACE(struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks));
rcu_dynticks_task_exit();
- smp_mb__before_atomic(); /* Force ordering w/previous sojourn. */
- atomic_inc(&rdtp->dynticks);
- /* CPUs seeing atomic_inc() must see later RCU read-side crit sects */
- smp_mb__after_atomic(); /* See above. */
- WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
- !(atomic_read(&rdtp->dynticks) & 0x1));
+ rcu_dynticks_eqs_exit();
rcu_cleanup_after_idle();
trace_rcu_dyntick(TPS("End"), oldval, rdtp->dynticks_nesting);
if (IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
@@ -1001,11 +1046,7 @@ void rcu_nmi_enter(void)
* period (observation due to Andy Lutomirski).
*/
if (!(atomic_read(&rdtp->dynticks) & 0x1)) {
- smp_mb__before_atomic(); /* Force delay from prior write. */
- atomic_inc(&rdtp->dynticks);
- /* atomic_inc() before later RCU read-side crit sects */
- smp_mb__after_atomic(); /* See above. */
- WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks) & 0x1));
+ rcu_dynticks_eqs_exit();
incby = 1;
}
rdtp->dynticks_nmi_nesting += incby;
@@ -1043,11 +1084,7 @@ void rcu_nmi_exit(void)
/* This NMI interrupted an RCU-idle CPU, restore RCU-idleness. */
rdtp->dynticks_nmi_nesting = 0;
- /* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */
- smp_mb__before_atomic(); /* See above. */
- atomic_inc(&rdtp->dynticks);
- smp_mb__after_atomic(); /* Force delay to next write. */
- WARN_ON_ONCE(atomic_read(&rdtp->dynticks) & 0x1);
+ rcu_dynticks_eqs_enter();
}
/**
@@ -3800,8 +3837,7 @@ rcu_init_percpu_data(int cpu, struct rcu_state *rsp)
init_callback_list(rdp); /* Re-enable callbacks on this CPU. */
rdp->dynticks->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
rcu_sysidle_init_percpu_data(rdp->dynticks);
- atomic_set(&rdp->dynticks->dynticks,
- (atomic_read(&rdp->dynticks->dynticks) & ~0x1) + 1);
+ rcu_dynticks_eqs_online();
raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
/*
--
2.5.2
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