srcu: Add data_race() to ->srcu_lock_count and ->srcu_unlock_count arrays

The srcu_data structure's ->srcu_lock_count and ->srcu_unlock_count arrays
are read and written locklessly, so this commit adds the data_race()
to the diagnostic-print loads from these arrays in order mark them as
known and approved data-racy accesses.

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@kernel.org>

diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index ba2b751..6d3ef70 100644 (file)
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -1281,8 +1281,8 @@ void srcu_torture_stats_print(struct srcu_struct *ssp, char *tt, char *tf)
                struct srcu_data *sdp;
 
                sdp = per_cpu_ptr(ssp->sda, cpu);
-               u0 = sdp->srcu_unlock_count[!idx];
-               u1 = sdp->srcu_unlock_count[idx];
+               u0 = data_race(sdp->srcu_unlock_count[!idx]);
+               u1 = data_race(sdp->srcu_unlock_count[idx]);
 
                /*
                 * Make sure that a lock is always counted if the corresponding
@@ -1290,8 +1290,8 @@ void srcu_torture_stats_print(struct srcu_struct *ssp, char *tt, char *tf)
                 */
                smp_rmb();
 
-               l0 = sdp->srcu_lock_count[!idx];
-               l1 = sdp->srcu_lock_count[idx];
+               l0 = data_race(sdp->srcu_lock_count[!idx]);
+               l1 = data_race(sdp->srcu_lock_count[idx]);
 
                c0 = l0 - u0;
                c1 = l1 - u1;