From: paulmck@kernel.org
To: rcu@vger.kernel.org
Cc: linux-kernel@vger.kernel.org, kernel-team@fb.com,
mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com,
akpm@linux-foundation.org, mathieu.desnoyers@efficios.com,
josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org,
rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com,
fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org,
"Paul E. McKenney" <paulmck@kernel.org>
Subject: [PATCH tip/core/rcu 09/11] rcu: Use READ_ONCE() for ->expmask in rcu_read_unlock_special()
Date: Mon, 9 Dec 2019 20:26:27 -0800 [thread overview]
Message-ID: <20191210042629.3808-9-paulmck@kernel.org> (raw)
In-Reply-To: <20191210042606.GA3624@paulmck-ThinkPad-P72>
From: "Paul E. McKenney" <paulmck@kernel.org>
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>
---
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 &&
--
2.9.5
next prev parent reply other threads:[~2019-12-10 4:26 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-10 4:26 [PATCH tip/core/rcu 0/11] Preemptible-RCU updates for v5.6 Paul E. McKenney
2019-12-10 4:26 ` [PATCH tip/core/rcu 01/11] rcu/nocb: Fix dump_tree hierarchy print always active paulmck
2019-12-10 4:26 ` [PATCH tip/core/rcu 02/11] rcu: Avoid data-race in rcu_gp_fqs_check_wake() paulmck
2019-12-10 4:26 ` [PATCH tip/core/rcu 03/11] rcu: Use lockdep rather than comment to enforce lock held paulmck
2019-12-10 4:26 ` [PATCH tip/core/rcu 04/11] rcu: Make PREEMPT_RCU be a modifier to TREE_RCU paulmck
2019-12-10 4:26 ` [PATCH tip/core/rcu 05/11] rcu: Use CONFIG_PREEMPTION where appropriate paulmck
2019-12-10 4:26 ` [PATCH tip/core/rcu 06/11] rcu: Rename some instance of CONFIG_PREEMPTION to CONFIG_PREEMPT_RCU paulmck
2019-12-10 4:26 ` [PATCH tip/core/rcu 07/11] rcu: Clear .exp_hint only when deferred quiescent state has been reported paulmck
2019-12-10 4:26 ` [PATCH tip/core/rcu 08/11] rcu: Clear ->rcu_read_unlock_special only once paulmck
2019-12-10 4:26 ` paulmck [this message]
2019-12-10 4:26 ` [PATCH tip/core/rcu 10/11] rcu: Provide wrappers for uses of ->rcu_read_lock_nesting paulmck
2019-12-10 4:26 ` [PATCH tip/core/rcu 11/11] rcu: Avoid tick_dep_set_cpu() misordering paulmck
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