From 3c345825c899df0751b01143b159ddaefb91a220 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Sat, 4 Mar 2017 12:33:53 -0800 Subject: rcu: Expedited wakeups need to be fully ordered Expedited grace periods use workqueue handlers that wake up the requesters, but there is no lock mediating this wakeup. Therefore, memory barriers are required to ensure that the handler's memory references are seen by all to occur before synchronize_*_expedited() returns to its caller. Possibly detected by syzkaller. Reported-by: Dmitry Vyukov Signed-off-by: Paul E. McKenney --- kernel/rcu/tree_exp.h | 2 ++ 1 file changed, 2 insertions(+) (limited to 'kernel/rcu') diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h index 51ca287828a2..027e123d93c7 100644 --- a/kernel/rcu/tree_exp.h +++ b/kernel/rcu/tree_exp.h @@ -533,6 +533,7 @@ static void rcu_exp_wait_wake(struct rcu_state *rsp, unsigned long s) rnp->exp_seq_rq = s; spin_unlock(&rnp->exp_lock); } + smp_mb(); /* All above changes before wakeup. */ wake_up_all(&rnp->exp_wq[(rsp->expedited_sequence >> 1) & 0x3]); } trace_rcu_exp_grace_period(rsp->name, s, TPS("endwake")); @@ -614,6 +615,7 @@ static void _synchronize_rcu_expedited(struct rcu_state *rsp, wait_event(rnp->exp_wq[(s >> 1) & 0x3], sync_exp_work_done(rsp, &rdp->exp_workdone0, s)); + smp_mb(); /* Workqueue actions happen before return. */ /* Let the next expedited grace period start. */ mutex_unlock(&rsp->exp_mutex); -- cgit v1.2.3