The following commit has been merged into the core/rcu branch of tip: Commit-ID: c51f83c315c392d9776c33eb16a2fe1349d65c7f Gitweb: https://git.kernel.org/tip/c51f83c315c392d9776c33eb16a2fe1349d65c7f Author: Paul E. McKenney <paulmck@xxxxxxxxxx> AuthorDate: Mon, 04 Nov 2019 08:22:45 -08:00 Committer: Paul E. McKenney <paulmck@xxxxxxxxxx> CommitterDate: Fri, 24 Jan 2020 10:27:33 -08:00 rcu: Use READ_ONCE() for ->expmask in rcu_read_unlock_special() The rcu_node structure's ->expmask field is updated only when holding the ->lock, but is also accessed locklessly. This means that all ->expmask updates must use WRITE_ONCE() and all reads carried out without holding ->lock must use READ_ONCE(). This commit therefore changes the lockless ->expmask read in rcu_read_unlock_special() to use READ_ONCE(). Reported-by: syzbot+99f4ddade3c22ab0cf23@xxxxxxxxxxxxxxxxxxxxxxxxx Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx> Acked-by: Marco Elver <elver@xxxxxxxxxx> --- kernel/rcu/tree_plugin.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index c3a3271..698a7f1 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -599,7 +599,7 @@ static void rcu_read_unlock_special(struct task_struct *t) struct rcu_node *rnp = rdp->mynode; exp = (t->rcu_blocked_node && t->rcu_blocked_node->exp_tasks) || - (rdp->grpmask & rnp->expmask) || + (rdp->grpmask & READ_ONCE(rnp->expmask)) || tick_nohz_full_cpu(rdp->cpu); // Need to defer quiescent state until everything is enabled. if (irqs_were_disabled && use_softirq &&
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