From: Sebastian Andrzej Siewior 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 --- 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(); } /**