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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2017-03-04 12:33:53 -0800
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2017-04-18 11:38:19 -0700
commit3c345825c899df0751b01143b159ddaefb91a220 (patch)
tree97675c609e2f160a43c96eb7a41acd2be94574bd /kernel
parent2e8c28c2dd96c6f1f2d454a4e4b928385841e247 (diff)
downloadop-kernel-dev-3c345825c899df0751b01143b159ddaefb91a220.zip
op-kernel-dev-3c345825c899df0751b01143b159ddaefb91a220.tar.gz
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 <dvyukov@google.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/rcu/tree_exp.h2
1 files changed, 2 insertions, 0 deletions
diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
index 51ca287..027e123 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);
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