[PATCH] rcutorture: Fix rcu_torture_pipe_update_one()/rcu_torture_writer() data race and concurrency bug

[linke li]

Some changes are done to fix a data race in commit 202489101f2e ("rcutorture: 
Fix rcu_torture_one_read()/rcu_torture_writer() data race")

 {
        int i;

-       i = rp->rtort_pipe_count;
+       i = READ_ONCE(rp->rtort_pipe_count);
        if (i > RCU_TORTURE_PIPE_LEN)
                i = RCU_TORTURE_PIPE_LEN;
        atomic_inc(&rcu_torture_wcount[i]);
-       if (++rp->rtort_pipe_count >= RCU_TORTURE_PIPE_LEN) {
+       WRITE_ONCE(rp->rtort_pipe_count, i + 1);
+       if (rp->rtort_pipe_count >= RCU_TORTURE_PIPE_LEN) {
                rp->rtort_mbtest = 0;
                return true;
        }

But ++rp->rtort_pipe_count is meant to add itself by 1, not give i+1 to
rp->rtort_pipe_count, because rp->rtort_pipe_count may write by
rcu_torture_writer() concurrently.

Also, rp->rtort_pipe_count in the next line should be read using
READ_ONCE() because of data race.

Signed-off-by: linke li <lilink...@qq.com>
---
 kernel/rcu/rcutorture.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index 7567ca8e743c..00059ace4fd5 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -465,8 +465,8 @@ rcu_torture_pipe_update_one(struct rcu_torture *rp)
        if (i > RCU_TORTURE_PIPE_LEN)
                i = RCU_TORTURE_PIPE_LEN;
        atomic_inc(&rcu_torture_wcount[i]);
-       WRITE_ONCE(rp->rtort_pipe_count, i + 1);
-       if (rp->rtort_pipe_count >= RCU_TORTURE_PIPE_LEN) {
+       WRITE_ONCE(rp->rtort_pipe_count, rp->rtort_pipe_count + 1);
+       if (READ_ONCE(rp->rtort_pipe_count) >= RCU_TORTURE_PIPE_LEN) {
                rp->rtort_mbtest = 0;
                return true;
        }
-- 
2.39.3 (Apple Git-145)