From: "Paul E. McKenney" <[email protected]>
[ Upstream commit 6040072f4774a575fa67b912efe7722874be337b ]
On powerpc systems, spinlock acquisition does not order prior stores
against later loads. This means that this statement:
rfcp->rfc_next = NULL;
Can be reordered to follow this statement:
WRITE_ONCE(*rfcpp, rfcp);
Which is then a data race with rcu_torture_fwd_prog_cr(), specifically,
this statement:
rfcpn = READ_ONCE(rfcp->rfc_next)
KCSAN located this data race, which represents a real failure on powerpc.
Signed-off-by: Paul E. McKenney <[email protected]>
Acked-by: Marco Elver <[email protected]>
Cc: Andrey Konovalov <[email protected]>
Cc: <[email protected]>
Signed-off-by: Sasha Levin <[email protected]>
---
kernel/rcu/rcutorture.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index 807fbf6123a77..251cead744603 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -2626,7 +2626,7 @@ static void rcu_torture_fwd_cb_cr(struct rcu_head *rhp)
spin_lock_irqsave(&rfp->rcu_fwd_lock, flags);
rfcpp = rfp->rcu_fwd_cb_tail;
rfp->rcu_fwd_cb_tail = &rfcp->rfc_next;
- WRITE_ONCE(*rfcpp, rfcp);
+ smp_store_release(rfcpp, rfcp);
WRITE_ONCE(rfp->n_launders_cb, rfp->n_launders_cb + 1);
i = ((jiffies - rfp->rcu_fwd_startat) / (HZ / FWD_CBS_HIST_DIV));
if (i >= ARRAY_SIZE(rfp->n_launders_hist))
--
2.43.0
