commit 65bfdd36c113f5d579a382d8f2847210ea4cdca6
author Paul E. McKenney <paulmck@kernel.org> Wed Jun 02 16:31:38 2021 -0700
committer Paul E. McKenney <paulmck@kernel.org> Fri Aug 06 13:41:48 2021 -0700
tree ce25f67a04bf28eb4db70074a4de34e6c614210a
parent b169246feb1d82dbee5f3f6a4ce57368644dce95

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@kernel.org>

include/linux/srcutiny.h

diff --git a/include/linux/srcutiny.h b/include/linux/srcutiny.h
index 0e0cf4d..6cfaa0a 100644
--- a/include/linux/srcutiny.h
+++ b/include/linux/srcutiny.h
@@ -61,7 +61,7 @@
 	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 @@
 {
 	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

kernel/rcu/srcutiny.c

diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c
index 26344dc..a0ba2ed49 100644
--- a/kernel/rcu/srcutiny.c
+++ b/kernel/rcu/srcutiny.c
@@ -96,7 +96,7 @@
  */
 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))