Commit 6040072f authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcutorture: Fix rcu_torture_fwd_cb_cr() data race 



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: default avatarPaul E. McKenney <paulmck@kernel.org>
Acked-by: default avatarMarco Elver <elver@google.com>
Cc: Andrey Konovalov <andreyknvl@gmail.com>
Cc: <kasan-dev@googlegroups.com>
parent 43b39caf

kernel/rcu/rcutorture.c

+1 −1
Original line number Diff line number Diff line
@@ -2630,7 +2630,7 @@ 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))