linux-kernel - [PATCH rcu 10/18] srcutiny: Mark read-side data races

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Message-Id: <20210721202127.2129660-10-paulmck@kernel.org>
Date:   Wed, 21 Jul 2021 13:21:18 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     rcu@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, kernel-team@...com, mingo@...nel.org,
        jiangshanlai@...il.com, akpm@...ux-foundation.org,
        mathieu.desnoyers@...icios.com, josh@...htriplett.org,
        tglx@...utronix.de, peterz@...radead.org, rostedt@...dmis.org,
        dhowells@...hat.com, edumazet@...gle.com, fweisbec@...il.com,
        oleg@...hat.com, joel@...lfernandes.org,
        "Paul E. McKenney" <paulmck@...nel.org>
Subject: [PATCH rcu 10/18] srcutiny: Mark read-side data races

This commit marks some interrupt-induced read-side data races in
__srcu_read_lock(), __srcu_read_unlock(), and srcu_torture_stats_print().

Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
---
 include/linux/srcutiny.h | 8 ++++----
 kernel/rcu/srcutiny.c    | 2 +-
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/include/linux/srcutiny.h b/include/linux/srcutiny.h
index 0e0cf4d6a72a0..6cfaa0a9a9b96 100644
--- a/include/linux/srcutiny.h
+++ b/include/linux/srcutiny.h
@@ -61,7 +61,7 @@ static inline int __srcu_read_lock(struct srcu_struct *ssp)
 	int idx;
 
 	idx = ((READ_ONCE(ssp->srcu_idx) + 1) & 0x2) >> 1;
-	WRITE_ONCE(ssp->srcu_lock_nesting[idx], ssp->srcu_lock_nesting[idx] + 1);
+	WRITE_ONCE(ssp->srcu_lock_nesting[idx], READ_ONCE(ssp->srcu_lock_nesting[idx]) + 1);
 	return idx;
 }
 
@@ -81,11 +81,11 @@ static inline void srcu_torture_stats_print(struct srcu_struct *ssp,
 {
 	int idx;
 
-	idx = ((READ_ONCE(ssp->srcu_idx) + 1) & 0x2) >> 1;
+	idx = ((data_race(READ_ONCE(ssp->srcu_idx)) + 1) & 0x2) >> 1;
 	pr_alert("%s%s Tiny SRCU per-CPU(idx=%d): (%hd,%hd)\n",
 		 tt, tf, idx,
-		 READ_ONCE(ssp->srcu_lock_nesting[!idx]),
-		 READ_ONCE(ssp->srcu_lock_nesting[idx]));
+		 data_race(READ_ONCE(ssp->srcu_lock_nesting[!idx])),
+		 data_race(READ_ONCE(ssp->srcu_lock_nesting[idx])));
 }
 
 #endif
diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c
index 26344dc6483b0..a0ba2ed49bc61 100644
--- a/kernel/rcu/srcutiny.c
+++ b/kernel/rcu/srcutiny.c
@@ -96,7 +96,7 @@ EXPORT_SYMBOL_GPL(cleanup_srcu_struct);
  */
 void __srcu_read_unlock(struct srcu_struct *ssp, int idx)
 {
-	int newval = ssp->srcu_lock_nesting[idx] - 1;
+	int newval = READ_ONCE(ssp->srcu_lock_nesting[idx]) - 1;
 
 	WRITE_ONCE(ssp->srcu_lock_nesting[idx], newval);
 	if (!newval && READ_ONCE(ssp->srcu_gp_waiting))
-- 
2.31.1.189.g2e36527f23