rcu-tasks: Make trc_read_check_handler() fetch ->trc_reader_nesting only once

This commit replaces the pair of READ_ONCE(t->trc_reader_nesting) calls
with a single such call and a local variable.  This makes the code's
intent more clear.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Neeraj Upadhyay <quic_neeraju@quicinc.com>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Martin KaFai Lau <kafai@fb.com>
Cc: KP Singh <kpsingh@kernel.org>

diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
index 561d24f..8fe78a7 100644 (file)
--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -1278,6 +1278,7 @@ static void trc_del_holdout(struct task_struct *t)
 /* IPI handler to check task state. */
 static void trc_read_check_handler(void *t_in)
 {
+       int nesting;
        struct task_struct *t = current;
        struct task_struct *texp = t_in;
 
@@ -1287,12 +1288,13 @@ static void trc_read_check_handler(void *t_in)
 
        // If the task is not in a read-side critical section, and
        // if this is the last reader, awaken the grace-period kthread.
-       if (likely(!READ_ONCE(t->trc_reader_nesting))) {
+       nesting = READ_ONCE(t->trc_reader_nesting);
+       if (likely(!nesting)) {
                rcu_trc_cmpxchg_need_qs(t, 0, TRC_NEED_QS_CHECKED);
                goto reset_ipi;
        }
        // If we are racing with an rcu_read_unlock_trace(), try again later.
-       if (unlikely(READ_ONCE(t->trc_reader_nesting) < 0))
+       if (unlikely(nesting < 0))
                goto reset_ipi;
 
        // Get here if the task is in a read-side critical section.  Set