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rcutorture: Fix rcu_torture_fwd_cb_cr() data race

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[ Upstream commit 6040072f47 ]

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 <paulmck@kernel.org>
Acked-by: Marco Elver <elver@google.com>
Cc: Andrey Konovalov <andreyknvl@gmail.com>
Cc: <kasan-dev@googlegroups.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Paul E. McKenney 2024-04-05 12:02:11 -07:00 committed by Greg Kroah-Hartman
parent 95cf80c934
commit 7adbf9b5c8
1 changed files with 1 additions and 1 deletions
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2
kernel/rcu/rcutorture.c
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@ -2592,7 +2592,7 @@ 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))