[PATCH 01/10] rcu: Directly lock rdp->nocb_lock on nocb code entrypoints

Frederic Weisbecker
2020-05-13T16:47:25Z

Pure NOCB code entrypoints (nocb_cb kthread, nocb_gp kthread, nocb
timers) can unconditionally lock rdp->nocb_lock as they always execute
in the context of an offloaded rdp.

This also prepare for toggling CPUs to/from callback's offloaded mode
where the offloaded state will possibly change when rdp->nocb_lock
isn't taken. We'll still want the entrypoints to lock the rdp in any
case.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Paul E. McKenney <paulmck@kernel.org>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Joel Fernandes <joel@joelfernandes.org>
---
kernel/rcu/tree_plugin.h | 14 +++++++-------
1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 097635c41135..523570469864 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -1909,7 +1909,7 @@ static void do_nocb_bypass_wakeup_timer(struct timer_list *t)
struct rcu_data *rdp = from_timer(rdp, t, nocb_bypass_timer);

trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("Timer"));
- rcu_nocb_lock_irqsave(rdp, flags);
+ raw_spin_lock_irqsave(&rdp->nocb_lock, flags);
smp_mb__after_spinlock(); /* Timer expire before wakeup. */
__call_rcu_nocb_wake(rdp, true, flags);
}
@@ -1942,7 +1942,7 @@ static void nocb_gp_wait(struct rcu_data *my_rdp)
*/
for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_cb_rdp) {
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("Check"));
- rcu_nocb_lock_irqsave(rdp, flags);
+ raw_spin_lock_irqsave(&rdp->nocb_lock, flags);
bypass_ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass);
if (bypass_ncbs &&
(time_after(j, READ_ONCE(rdp->nocb_bypass_first) + 1) ||
@@ -1951,7 +1951,7 @@ static void nocb_gp_wait(struct rcu_data *my_rdp)
(void)rcu_nocb_try_flush_bypass(rdp, j);
bypass_ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass);
} else if (!bypass_ncbs && rcu_segcblist_empty(&rdp->cblist)) {
- rcu_nocb_unlock_irqrestore(rdp, flags);
+ raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
continue; /* No callbacks here, try next. */
}
if (bypass_ncbs) {
@@ -1996,7 +1996,7 @@ static void nocb_gp_wait(struct rcu_data *my_rdp)
} else {
needwake = false;
}
- rcu_nocb_unlock_irqrestore(rdp, flags);
+ raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
if (needwake) {
swake_up_one(&rdp->nocb_cb_wq);
gotcbs = true;
@@ -2084,7 +2084,7 @@ static void nocb_cb_wait(struct rcu_data *rdp)
rcu_do_batch(rdp);
local_bh_enable();
lockdep_assert_irqs_enabled();
- rcu_nocb_lock_irqsave(rdp, flags);
+ raw_spin_lock_irqsave(&rdp->nocb_lock, flags);
if (rcu_segcblist_nextgp(&rdp->cblist, &cur_gp_seq) &&
rcu_seq_done(&rnp->gp_seq, cur_gp_seq) &&
raw_spin_trylock_rcu_node(rnp)) { /* irqs already disabled. */
@@ -2092,7 +2092,7 @@ static void nocb_cb_wait(struct rcu_data *rdp)
raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
}
if (rcu_segcblist_ready_cbs(&rdp->cblist)) {
- rcu_nocb_unlock_irqrestore(rdp, flags);
+ raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
if (needwake_gp)
rcu_gp_kthread_wake();
return;
@@ -2100,7 +2100,7 @@ static void nocb_cb_wait(struct rcu_data *rdp)

trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("CBSleep"));
WRITE_ONCE(rdp->nocb_cb_sleep, true);
- rcu_nocb_unlock_irqrestore(rdp, flags);
+ raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
if (needwake_gp)
rcu_gp_kthread_wake();
swait_event_interruptible_exclusive(rdp->nocb_cb_wq,
--
2.25.0