| From c51f83c315c392d9776c33eb16a2fe1349d65c7f Mon Sep 17 00:00:00 2001 |
| From: "Paul E. McKenney" <paulmck@kernel.org> |
| Date: Mon, 4 Nov 2019 08:22:45 -0800 |
| Subject: rcu: Use READ_ONCE() for ->expmask in rcu_read_unlock_special() |
| |
| From: Paul E. McKenney <paulmck@kernel.org> |
| |
| commit c51f83c315c392d9776c33eb16a2fe1349d65c7f upstream. |
| |
| 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@syzkaller.appspotmail.com |
| Signed-off-by: Paul E. McKenney <paulmck@kernel.org> |
| Acked-by: Marco Elver <elver@google.com> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| |
| --- |
| kernel/rcu/tree_plugin.h | 2 +- |
| 1 file changed, 1 insertion(+), 1 deletion(-) |
| |
| --- a/kernel/rcu/tree_plugin.h |
| +++ b/kernel/rcu/tree_plugin.h |
| @@ -612,7 +612,7 @@ static void rcu_read_unlock_special(stru |
| |
| t->rcu_read_unlock_special.b.exp_hint = false; |
| 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 && |
