1 files changed, 101 insertions, 0 deletions
diff --git a/debian/patches-rt/percpu-refcount-use-normal-instead-of-RCU-sched.patch b/debian/patches-rt/percpu-refcount-use-normal-instead-of-RCU-sched.patch
new file mode 100644
index 000000000..0ee0b78d8
--- /dev/null
+++ b/debian/patches-rt/percpu-refcount-use-normal-instead-of-RCU-sched.patch
@@ -0,0 +1,101 @@
+From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
+Date: Wed, 4 Sep 2019 17:59:36 +0200
+Subject: [PATCH] percpu-refcount: use normal instead of RCU-sched"
+MIME-Version: 1.0
+Content-Type: text/plain; charset=UTF-8
+Content-Transfer-Encoding: 8bit
+Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/5.4/older/patches-5.4.3-rt1.tar.xz
+
+This is a revert of commit
+   a4244454df129 ("percpu-refcount: use RCU-sched insted of normal RCU")
+
+which claims the only reason for using RCU-sched is
+   "rcu_read_[un]lock() … are slightly more expensive than preempt_disable/enable()"
+
+and
+    "As the RCU critical sections are extremely short, using sched-RCU
+    shouldn't have any latency implications."
+
+The problem with RCU-sched is that it disables preemption and the
+callback must not acquire any sleeping locks like spinlock_t on
+PREEMPT_RT which is the case.
+
+Convert back to normal RCU.
+
+Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
+---
+ include/linux/percpu-refcount.h |   16 ++++++++--------
+ 1 file changed, 8 insertions(+), 8 deletions(-)
+
+--- a/include/linux/percpu-refcount.h
++++ b/include/linux/percpu-refcount.h
+@@ -186,14 +186,14 @@ static inline void percpu_ref_get_many(s
+ {
+ 	unsigned long __percpu *percpu_count;
+ 
+-	rcu_read_lock_sched();
++	rcu_read_lock();
+ 
+ 	if (__ref_is_percpu(ref, &percpu_count))
+ 		this_cpu_add(*percpu_count, nr);
+ 	else
+ 		atomic_long_add(nr, &ref->count);
+ 
+-	rcu_read_unlock_sched();
++	rcu_read_unlock();
+ }
+ 
+ /**
+@@ -223,7 +223,7 @@ static inline bool percpu_ref_tryget(str
+ 	unsigned long __percpu *percpu_count;
+ 	bool ret;
+ 
+-	rcu_read_lock_sched();
++	rcu_read_lock();
+ 
+ 	if (__ref_is_percpu(ref, &percpu_count)) {
+ 		this_cpu_inc(*percpu_count);
+@@ -232,7 +232,7 @@ static inline bool percpu_ref_tryget(str
+ 		ret = atomic_long_inc_not_zero(&ref->count);
+ 	}
+ 
+-	rcu_read_unlock_sched();
++	rcu_read_unlock();
+ 
+ 	return ret;
+ }
+@@ -257,7 +257,7 @@ static inline bool percpu_ref_tryget_liv
+ 	unsigned long __percpu *percpu_count;
+ 	bool ret = false;
+ 
+-	rcu_read_lock_sched();
++	rcu_read_lock();
+ 
+ 	if (__ref_is_percpu(ref, &percpu_count)) {
+ 		this_cpu_inc(*percpu_count);
+@@ -266,7 +266,7 @@ static inline bool percpu_ref_tryget_liv
+ 		ret = atomic_long_inc_not_zero(&ref->count);
+ 	}
+ 
+-	rcu_read_unlock_sched();
++	rcu_read_unlock();
+ 
+ 	return ret;
+ }
+@@ -285,14 +285,14 @@ static inline void percpu_ref_put_many(s
+ {
+ 	unsigned long __percpu *percpu_count;
+ 
+-	rcu_read_lock_sched();
++	rcu_read_lock();
+ 
+ 	if (__ref_is_percpu(ref, &percpu_count))
+ 		this_cpu_sub(*percpu_count, nr);
+ 	else if (unlikely(atomic_long_sub_and_test(nr, &ref->count)))
+ 		ref->release(ref);
+ 
+-	rcu_read_unlock_sched();
++	rcu_read_unlock();
+ }
+ 
+ /**