> -----Original Message-----
> From: Neil Horman [mailto:nhorman at tuxdriver.com]
> Sent: Thursday, September 18, 2014 18:03
> To: Wodkowski, PawelX
> Cc: dev at dpdk.org; Jastrzebski, MichalX K; Doherty, Declan
> Subject: Re: [dpdk-dev] [PATCH 2/2] bond: add mode 4 support
>
> On Thu, Sep 18, 2014 at 08:07:31AM +0000, Wodkowski, PawelX wrote:
> > > > +int
> > > > +bond_mode_8023ad_deactivate_slave(struct rte_eth_dev *bond_dev,
> > > > + uint8_t slave_pos)
> > > > +{
> > > > + struct bond_dev_private *internals =
> > > > bond_dev->data->dev_private;
> > > > + struct mode8023ad_data *data = &internals->mode4;
> > > > + struct port *port;
> > > > + uint8_t i;
> > > > +
> > > > + bond_mode_8023ad_stop(bond_dev);
> > > > +
> > > > + /* Exclude slave from transmit policy. If this slave is an
> > > > aggregator
> > > > + * make all aggregated slaves unselected to force sellection
> > > > logic
> > > > + * to select suitable aggregator for this port */
> > > > + for (i = 0; i < internals->active_slave_count; i++) {
> > > > + port = &data->port_list[slave_pos];
> > > > + if (port->used_agregator_idx == slave_pos) {
> > > > + port->selected = UNSELECTED;
> > > > + port->actor_state &= ~(STATE_SYNCHRONIZATION |
> > > STATE_DISTRIBUTING |
> > > > + STATE_COLLECTING);
> > > > +
> > > > + /* Use default aggregator */
> > > > + port->used_agregator_idx = i;
> > > > + }
> > > > + }
> > > > +
> > > > + port = &data->port_list[slave_pos];
> > > > + timer_cancel(&port->current_while_timer);
> > > > + timer_cancel(&port->periodic_timer);
> > > > + timer_cancel(&port->wait_while_timer);
> > > > + timer_cancel(&port->tx_machine_timer);
> > > > +
> > > These all seem rather racy. Alarm callbacks are executed with the alarm
> > > list
> > > locks not held. So there is every possibility that you could execute
> > > these (or
> > > any timer_cancel calls in this PMD in parallel with the internal state
> > > machine
> > > timer callback, and leave either with a corrupted timer list (resulting
> > > from a
> > > double free between here, and the actual callback site),
> >
> > I don't think so. Yes, callbacks are executed with alarm list locks not
> > held, but
> > this is not the issue because access to list itself is guarded by lock and
> > ap->executing variable. So list will not be trashed. Check source of
> > eal_alarm_callback(), rte_eal_alarm_set() and rte_eal_alarm_cancel().
> >
> Yes, you're right, the list is probably safe wht the executing bit.
>
> > > or a timer that is
> > > actually still pending when a slave is removed.
> > >
> > This is not the issue also, but problem might be similar. I assumed that
> > alarms
> > are atomic but when I looked at rte alarms closer I saw a race condition
> > between and rte_eal_alarm_cancel() from bond_mode_8023ad_stop()
> > and rte_eal_alarm_set() from state machines callback. This need to be
> > reworked in some way.
>
> Yes, this is what I was referring to:
>
> CPU0 CPU1
> rte_eal_alarm_callback bond_8023ad_deactivate_slave
> -bond_8023_ad_periodic_cb timer_cancel
> timer_set
>
> If those timer functions operate on the same timer, the result is that you can
> leave the stop/deactivate slave paths with a timer function for that slave
> still
> pending. The bonding mode needs some internal state to serialize those
> operations and determine if the timer should be reactivated.
>
> Neil
I did rethink the issue and problem is much simpler than it looks like. I did
the
following:
1. Change internal state machine alarms to use rte_rdtsc(). This makes all
mode 4 internal timer_*() function not affected by any race condition.
2. Do a busy loop when canceling main callback timer until cancel is
successfull.
This should do the trick about race condition. Do you agree?
Here is part involving timers I have changed:
static void
-timer_expired_cb(void *arg)
+timer_stop(uint64_t *timer)
{
- enum timer_state *timer = arg;
-
- BOND_ASSERT(*timer == TIMER_RUNNING);
- *timer = TIMER_EXPIRED;
+ *timer = 0;
}
static void
-timer_cancel(enum timer_state *timer)
+timer_set(uint64_t *timer, uint64_t timeout_ms)
{
- rte_eal_alarm_cancel(&timer_expired_cb, timer);
- *timer = TIMER_NOT_STARTED;
+ *timer = rte_rdtsc() + timeout_ms * rte_get_tsc_hz() / 1000;
}
+/* Forces given timer to be in expired state. */
static void
-timer_set(enum timer_state *timer, uint64_t timeout)
+timer_force_expired(uint64_t *timer)
{
- rte_eal_alarm_cancel(&timer_expired_cb, timer);
- rte_eal_alarm_set(timeout * 1000, &timer_expired_cb, timer);
- *timer = TIMER_RUNNING;
+ *timer = rte_rdtsc();
}
static bool
-timer_is_expired(enum timer_state *timer)
+timer_is_stopped(uint64_t *timer)
{
- return *timer == TIMER_EXPIRED;
+ return *timer == 0;
+}
+
+/* Timer is in running state if it is not stopped nor expired */
+static bool
+timer_is_running(uint64_t *timer)
+{
+ return *timer > 0 && *timer < rte_rdtsc();
+}
+
+
+static bool
+timer_is_expired(uint64_t *timer)
+{
+ return *timer <= rte_rdtsc();
}
---
And part stopping mode 4 callback.
-int
+void
bond_mode_8023ad_stop(struct rte_eth_dev *bond_dev)
{
- rte_eal_alarm_cancel(bond_mode_8023ad_periodic_cb, bond_dev);
- return 0;
+ /* Loop untill we cancel pending alarm. Alarm that is executing will
+ * not be canceled but when reshedules it self it will be canceled. */
+ while (rte_eal_alarm_cancel(&bond_mode_8023ad_periodic_cb, bond_dev) ==
0)
+ rte_pause();
}
