[PATCH rcu 07/32] rcu-tasks: Make trc_read_check_handler() fetch ->trc_reader_nesting only once

Paul E. McKenney
2022-06-20T22:55:41Z

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>
---
kernel/rcu/tasks.h | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
index 561d24f7f73cc..8fe78a7fecafd 100644
--- 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
--
2.31.1.189.g2e36527f23