rcu/nocb: Shutdown nocb timer on de-offloading

This commit ensures that the nocb timer is shut down before reaching the
final de-offloaded state.  The key goal is to prevent the timer handler
from manipulating the callbacks without the protection of the nocb locks.

Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Neeraj Upadhyay <neeraju@codeaurora.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Inspired-by: Paul E. McKenney <paulmck@kernel.org>
Tested-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index e0deb48..5d359b9 100644 (file)
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -257,6 +257,7 @@ struct rcu_data {
 };
 
 /* Values for nocb_defer_wakeup field in struct rcu_data. */
+#define RCU_NOCB_WAKE_OFF      -1
 #define RCU_NOCB_WAKE_NOT      0
 #define RCU_NOCB_WAKE          1
 #define RCU_NOCB_WAKE_FORCE    2

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 03ae1ce..c88ad62 100644 (file)
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -1665,6 +1665,8 @@ static void wake_nocb_gp(struct rcu_data *rdp, bool force,
 static void wake_nocb_gp_defer(struct rcu_data *rdp, int waketype,
                               const char *reason)
 {
+       if (rdp->nocb_defer_wakeup == RCU_NOCB_WAKE_OFF)
+               return;
        if (rdp->nocb_defer_wakeup == RCU_NOCB_WAKE_NOT)
                mod_timer(&rdp->nocb_timer, jiffies + 1);
        if (rdp->nocb_defer_wakeup < waketype)
@@ -2243,7 +2245,7 @@ static int rcu_nocb_cb_kthread(void *arg)
 /* Is a deferred wakeup of rcu_nocb_kthread() required? */
 static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp)
 {
-       return READ_ONCE(rdp->nocb_defer_wakeup);
+       return READ_ONCE(rdp->nocb_defer_wakeup) > RCU_NOCB_WAKE_NOT;
 }
 
 /* Do a deferred wakeup of rcu_nocb_kthread(). */
@@ -2337,6 +2339,12 @@ static int __rcu_nocb_rdp_deoffload(struct rcu_data *rdp)
        swait_event_exclusive(rdp->nocb_state_wq,
                              !rcu_segcblist_test_flags(cblist, SEGCBLIST_KTHREAD_CB |
                                                        SEGCBLIST_KTHREAD_GP));
+       /* Make sure nocb timer won't stay around */
+       rcu_nocb_lock_irqsave(rdp, flags);
+       WRITE_ONCE(rdp->nocb_defer_wakeup, RCU_NOCB_WAKE_OFF);
+       rcu_nocb_unlock_irqrestore(rdp, flags);
+       del_timer_sync(&rdp->nocb_timer);
+
        return ret;
 }
 
@@ -2394,6 +2402,8 @@ static int __rcu_nocb_rdp_offload(struct rcu_data *rdp)
         * SEGCBLIST_SOFTIRQ_ONLY mode.
         */
        raw_spin_lock_irqsave(&rdp->nocb_lock, flags);
+       /* Re-enable nocb timer */
+       WRITE_ONCE(rdp->nocb_defer_wakeup, RCU_NOCB_WAKE_NOT);
        /*
         * We didn't take the nocb lock while working on the
         * rdp->cblist in SEGCBLIST_SOFTIRQ_ONLY mode.