[tip: core/rcu] rcutorture: Emulate dyntick aspect of userspace nohz_full sojourn

[tip-bot2 for Paul E. McKenney]

The following commit has been merged into the core/rcu branch of tip:

Commit-ID:     79ba7ff5a9925f5c170f51ed7a96d1475eb6c27f
Gitweb:        https://git.kernel.org/tip/79ba7ff5a9925f5c170f51ed7a96d1475eb6c27f
Author:        Paul E. McKenney <paulmck@xxxxxxxxxx>
AuthorDate:    Sun, 04 Aug 2019 13:17:35 -07:00
Committer:     Paul E. McKenney <paulmck@xxxxxxxxxx>
CommitterDate: Sat, 05 Oct 2019 10:46:05 -07:00

rcutorture: Emulate dyntick aspect of userspace nohz_full sojourn

During an actual call_rcu() flood, there would be frequent trips to
userspace (in-kernel call_rcu() floods must be otherwise housebroken).
Userspace execution on nohz_full CPUs implies an RCU dyntick idle/not-idle
transition pair, so this commit adds emulation of that pair.

Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
---
 include/linux/rcutiny.h |  1 +
 kernel/rcu/rcutorture.c | 11 +++++++++++
 kernel/rcu/tree.c       |  1 +
 3 files changed, 13 insertions(+)

diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
index 9bf1dfe..37b6f0c 100644
--- a/include/linux/rcutiny.h
+++ b/include/linux/rcutiny.h
@@ -84,6 +84,7 @@ static inline void rcu_scheduler_starting(void) { }
 #endif /* #else #ifndef CONFIG_SRCU */
 static inline void rcu_end_inkernel_boot(void) { }
 static inline bool rcu_is_watching(void) { return true; }
+static inline void rcu_momentary_dyntick_idle(void) { }
 
 /* Avoid RCU read-side critical sections leaking across. */
 static inline void rcu_all_qs(void) { barrier(); }
diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index ab61f5c..49ad887 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -1761,6 +1761,11 @@ static unsigned long rcu_torture_fwd_prog_cbfree(void)
 		kfree(rfcp);
 		freed++;
 		rcu_torture_fwd_prog_cond_resched(freed);
+		if (tick_nohz_full_enabled()) {
+			local_irq_save(flags);
+			rcu_momentary_dyntick_idle();
+			local_irq_restore(flags);
+		}
 	}
 	return freed;
 }
@@ -1835,6 +1840,7 @@ static void rcu_torture_fwd_prog_nr(int *tested, int *tested_tries)
 static void rcu_torture_fwd_prog_cr(void)
 {
 	unsigned long cver;
+	unsigned long flags;
 	unsigned long gps;
 	int i;
 	long n_launders;
@@ -1894,6 +1900,11 @@ static void rcu_torture_fwd_prog_cr(void)
 		}
 		cur_ops->call(&rfcp->rh, rcu_torture_fwd_cb_cr);
 		rcu_torture_fwd_prog_cond_resched(n_launders + n_max_cbs);
+		if (tick_nohz_full_enabled()) {
+			local_irq_save(flags);
+			rcu_momentary_dyntick_idle();
+			local_irq_restore(flags);
+		}
 	}
 	stoppedat = jiffies;
 	n_launders_cb_snap = READ_ONCE(n_launders_cb);
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 7c67ea5..66354ef 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -375,6 +375,7 @@ void rcu_momentary_dyntick_idle(void)
 	WARN_ON_ONCE(!(special & RCU_DYNTICK_CTRL_CTR));
 	rcu_preempt_deferred_qs(current);
 }
+EXPORT_SYMBOL_GPL(rcu_momentary_dyntick_idle);
 
 /**
  * rcu_is_cpu_rrupt_from_idle - see if interrupted from idle