From af2789db13b8dc38d16e969f8c11b9468be42d46 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Tue, 26 May 2020 11:22:03 -0700 Subject: [PATCH] refperf: Convert reader_task structure's "start" field to int This commit converts the reader_task structure's "start" field to int in order to demote a full barrier to an smp_load_acquire() and also to simplify the code a bit. While in the area, and to enlist the compiler's help in ensuring that nothing was missed, the field's name was changed to start_reader. Also while in the area, change the main_func() store to use smp_store_release() to further fortify against wait/wake races. Cc: Joel Fernandes (Google) Signed-off-by: Paul E. McKenney --- kernel/rcu/refperf.c | 9 ++++----- 1 file changed, 4 insertions(+), 5 deletions(-) diff --git a/kernel/rcu/refperf.c b/kernel/rcu/refperf.c index 8815ccfb6f98..2fd3ed1a0d0d 100644 --- a/kernel/rcu/refperf.c +++ b/kernel/rcu/refperf.c @@ -80,7 +80,7 @@ torture_param(bool, shutdown, REFPERF_SHUTDOWN, struct reader_task { struct task_struct *task; - atomic_t start; + int start_reader; wait_queue_head_t wq; u64 last_duration_ns; }; @@ -243,7 +243,7 @@ ref_perf_reader(void *arg) VERBOSE_PERFOUT("ref_perf_reader %ld: waiting to start next experiment on cpu %d", me, smp_processor_id()); // Wait for signal that this reader can start. - wait_event(rt->wq, (atomic_read(&nreaders_exp) && atomic_read(&rt->start)) || + wait_event(rt->wq, (atomic_read(&nreaders_exp) && smp_load_acquire(&rt->start_reader)) || torture_must_stop()); if (torture_must_stop()) @@ -252,8 +252,7 @@ ref_perf_reader(void *arg) // Make sure that the CPU is affinitized appropriately during testing. WARN_ON_ONCE(smp_processor_id() != me); - smp_mb__before_atomic(); - atomic_dec(&rt->start); + WRITE_ONCE(rt->start_reader, 0); VERBOSE_PERFOUT("ref_perf_reader %ld: experiment %d started", me, exp_idx); @@ -372,7 +371,7 @@ static int main_func(void *arg) exp_idx = exp; for (r = 0; r < nreaders; r++) { - atomic_set(&reader_tasks[r].start, 1); + smp_store_release(&reader_tasks[r].start_reader, 1); wake_up(&reader_tasks[r].wq); }