[tip: core/rcu] rcutorture: Annotation lockless accesses to rcu_torture_current

[tip-bot2 for Paul E. McKenney]

The following commit has been merged into the core/rcu branch of tip:

Commit-ID:     5396d31d3a396039502f75a128bd8064819cba61
Gitweb:        https://git.kernel.org/tip/5396d31d3a396039502f75a128bd8064819cba61
Author:        Paul E. McKenney <paulmck@xxxxxxxxxx>
AuthorDate:    Wed, 08 Jan 2020 19:58:13 -08:00
Committer:     Paul E. McKenney <paulmck@xxxxxxxxxx>
CommitterDate: Thu, 20 Feb 2020 16:03:31 -08:00

rcutorture: Annotation lockless accesses to rcu_torture_current

The rcutorture global variable rcu_torture_current is accessed locklessly,
so it must use the RCU pointer load/store primitives.  This commit
therefore adds several that were missed.

This data race was reported by KCSAN.  Not appropriate for backporting due
to failure being unlikely and due to this being used only by rcutorture.

Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
---
 kernel/rcu/rcutorture.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index 0b9ce9a..7e01e9a 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -1407,6 +1407,7 @@ rcu_torture_stats_print(void)
 	int i;
 	long pipesummary[RCU_TORTURE_PIPE_LEN + 1] = { 0 };
 	long batchsummary[RCU_TORTURE_PIPE_LEN + 1] = { 0 };
+	struct rcu_torture *rtcp;
 	static unsigned long rtcv_snap = ULONG_MAX;
 	static bool splatted;
 	struct task_struct *wtp;
@@ -1423,10 +1424,10 @@ rcu_torture_stats_print(void)
 	}
 
 	pr_alert("%s%s ", torture_type, TORTURE_FLAG);
+	rtcp = rcu_access_pointer(rcu_torture_current);
 	pr_cont("rtc: %p %s: %lu tfle: %d rta: %d rtaf: %d rtf: %d ",
-		rcu_torture_current,
-		rcu_torture_current && !rcu_stall_is_suppressed_at_boot()
-			? "ver" : "VER",
+		rtcp,
+		rtcp && !rcu_stall_is_suppressed_at_boot() ? "ver" : "VER",
 		rcu_torture_current_version,
 		list_empty(&rcu_torture_freelist),
 		atomic_read(&n_rcu_torture_alloc),
@@ -1482,7 +1483,8 @@ rcu_torture_stats_print(void)
 	if (cur_ops->stats)
 		cur_ops->stats();
 	if (rtcv_snap == rcu_torture_current_version &&
-	    rcu_torture_current != NULL && !rcu_stall_is_suppressed()) {
+	    rcu_access_pointer(rcu_torture_current) &&
+	    !rcu_stall_is_suppressed()) {
 		int __maybe_unused flags = 0;
 		unsigned long __maybe_unused gp_seq = 0;