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dpif-netdev: Fix crash in dpif_netdev_execute().
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dp_netdev_get_pmd() is allowed to return NULL (even if we call it with
NON_PMD_CORE_ID) for different reasons:

* Since we use RCU to protect pmd threads, it is possible that
  ovs_refcount_try_ref_rcu() has failed.
* During reconfiguration we destroy every thread.

This commit makes sure that we always handle the case when
dp_netdev_get_pmd() returns NULL without crashing (the change in
dpif_netdev_run() doesn't fix anything, because everything is happening
in the main thread, but it's better to honor the interface in case we
change our threading model).

This actually fixes a pretty serious crash that happens if
dpif_netdev_execute() is called from a non pmd thread while
reconfiguration is happening.  It can be triggered by enabling bfd
(because it's handled by the monitor thread, which is a non pmd thread)
on an interface and changing something that requires datapath
reconfiguration (n_rxq, pmd-cpu-mask, mtu).

A testcase that reproduces the race condition is included.

This is a possible backtrace of the segfault:

 #0  0x000000000060c7f1 in dp_execute_cb (aux_=0x7f1dd2d2a320,
 packets_=0x7f1dd2d2a370, a=0x7f1dd2d2a658, may_steal=false) at
 ../lib/dpif-netdev.c:4357
 #1  0x00000000006448b2 in odp_execute_actions (dp=0x7f1dd2d2a320,
 batch=0x7f1dd2d2a370, steal=false, actions=0x7f1dd2d2a658,
 actions_len=8,
     dp_execute_action=0x60c7a5 <dp_execute_cb>) at
 ../lib/odp-execute.c:538
 #2  0x000000000060d00c in dp_netdev_execute_actions (pmd=0x0,
 packets=0x7f1dd2d2a370, may_steal=false, flow=0x7f1dd2d2ae70,
 actions=0x7f1dd2d2a658, actions_len=8,
     now=44965873) at ../lib/dpif-netdev.c:4577
 #3  0x000000000060834a in dpif_netdev_execute (dpif=0x2b67b70,
 execute=0x7f1dd2d2a578) at ../lib/dpif-netdev.c:2624
 #4  0x0000000000608441 in dpif_netdev_operate (dpif=0x2b67b70,
 ops=0x7f1dd2d2a5c8, n_ops=1) at ../lib/dpif-netdev.c:2654
 #5  0x0000000000610a30 in dpif_operate (dpif=0x2b67b70,
 ops=0x7f1dd2d2a5c8, n_ops=1) at ../lib/dpif.c:1268
 #6  0x000000000061098c in dpif_execute (dpif=0x2b67b70,
 execute=0x7f1dd2d2aa50) at ../lib/dpif.c:1233
 #7  0x00000000005b9008 in ofproto_dpif_execute_actions__
 (ofproto=0x2b69360, version=18446744073709551614, flow=0x7f1dd2d2ae70,
 rule=0x0, ofpacts=0x7f1dd2d2b100,
     ofpacts_len=16, indentation=0, depth=0, resubmits=0,
 packet=0x7f1dd2d2b5c0) at ../ofproto/ofproto-dpif.c:3806
 #8  0x00000000005b907a in ofproto_dpif_execute_actions
 (ofproto=0x2b69360, version=18446744073709551614, flow=0x7f1dd2d2ae70,
 rule=0x0, ofpacts=0x7f1dd2d2b100,
     ofpacts_len=16, packet=0x7f1dd2d2b5c0) at
 ../ofproto/ofproto-dpif.c:3823
 #9  0x00000000005dea9b in xlate_send_packet (ofport=0x2b98380,
 oam=false, packet=0x7f1dd2d2b5c0) at
 ../ofproto/ofproto-dpif-xlate.c:5792
 #10 0x00000000005bab12 in ofproto_dpif_send_packet (ofport=0x2b98380,
 oam=false, packet=0x7f1dd2d2b5c0) at ../ofproto/ofproto-dpif.c:4628
 #11 0x00000000005c3fc8 in monitor_mport_run (mport=0x2b8cd00,
 packet=0x7f1dd2d2b5c0) at ../ofproto/ofproto-dpif-monitor.c:287
 #12 0x00000000005c3d9b in monitor_run () at
 ../ofproto/ofproto-dpif-monitor.c:227
 #13 0x00000000005c3cab in monitor_main (args=0x0) at
 ../ofproto/ofproto-dpif-monitor.c:189
 #14 0x00000000006a183a in ovsthread_wrapper (aux_=0x2b8afd0) at
 ../lib/ovs-thread.c:342
 #15 0x00007f1dd75eb444 in start_thread (arg=0x7f1dd2d2c700) at
 pthread_create.c:333
 #16 0x00007f1dd6e1d20d in clone () at
 ../sysdeps/unix/sysv/linux/x86_64/clone.S:109

Signed-off-by: Daniele Di Proietto <[email protected]>
Acked-by: Ben Pfaff <[email protected]>
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@ddiproietto
ddiproietto committed Oct 12, 2016
1 parent 888e071 commit 546e57d
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Showing 2 changed files with 58 additions and 13 deletions.
33 changes: 20 additions & 13 deletions lib/dpif-netdev.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -2602,6 +2602,9 @@ dpif_netdev_execute(struct dpif *dpif, struct dpif_execute *execute)
pmd = ovsthread_getspecific(dp->per_pmd_key);
if (!pmd) {
pmd = dp_netdev_get_pmd(dp, NON_PMD_CORE_ID);
if (!pmd) {
return EBUSY;
}
}

/* If the current thread is non-pmd thread, acquires
Expand Down Expand Up @@ -2967,25 +2970,28 @@ dpif_netdev_run(struct dpif *dpif)
{
struct dp_netdev_port *port;
struct dp_netdev *dp = get_dp_netdev(dpif);
struct dp_netdev_pmd_thread *non_pmd = dp_netdev_get_pmd(dp,
NON_PMD_CORE_ID);
struct dp_netdev_pmd_thread *non_pmd;
uint64_t new_tnl_seq;

ovs_mutex_lock(&dp->port_mutex);
ovs_mutex_lock(&dp->non_pmd_mutex);
HMAP_FOR_EACH (port, node, &dp->ports) {
if (!netdev_is_pmd(port->netdev)) {
int i;
non_pmd = dp_netdev_get_pmd(dp, NON_PMD_CORE_ID);
if (non_pmd) {
ovs_mutex_lock(&dp->non_pmd_mutex);
HMAP_FOR_EACH (port, node, &dp->ports) {
if (!netdev_is_pmd(port->netdev)) {
int i;

for (i = 0; i < port->n_rxq; i++) {
dp_netdev_process_rxq_port(non_pmd, port, port->rxqs[i].rxq);
for (i = 0; i < port->n_rxq; i++) {
dp_netdev_process_rxq_port(non_pmd, port,
port->rxqs[i].rxq);
}
}
}
}
dpif_netdev_xps_revalidate_pmd(non_pmd, time_msec(), false);
ovs_mutex_unlock(&dp->non_pmd_mutex);
dpif_netdev_xps_revalidate_pmd(non_pmd, time_msec(), false);
ovs_mutex_unlock(&dp->non_pmd_mutex);

dp_netdev_pmd_unref(non_pmd);
dp_netdev_pmd_unref(non_pmd);
}

if (dp_netdev_is_reconf_required(dp) || ports_require_restart(dp)) {
reconfigure_pmd_threads(dp);
Expand Down Expand Up @@ -3189,7 +3195,8 @@ dp_netdev_pmd_reload_done(struct dp_netdev_pmd_thread *pmd)
}

/* Finds and refs the dp_netdev_pmd_thread on core 'core_id'. Returns
* the pointer if succeeds, otherwise, NULL.
* the pointer if succeeds, otherwise, NULL (it can return NULL even if
* 'core_id' is NON_PMD_CORE_ID).
*
* Caller must unrefs the returned reference. */
static struct dp_netdev_pmd_thread *
Expand Down
38 changes: 38 additions & 0 deletions tests/pmd.at
View file
Original file line number Diff line number Diff line change
Expand Up @@ -516,3 +516,41 @@ p1 3 0 2

OVS_VSWITCHD_STOP(["/dpif_netdev|WARN|There is no PMD thread on core/d"])
AT_CLEANUP

AT_SETUP([PMD - monitor threads])
OVS_VSWITCHD_START(
[], [], [], [--dummy-numa 0,0])
AT_CHECK([ovs-appctl vlog/set dpif:dbg dpif_netdev:dbg])

dnl The two devices are connected together externally using net.sock
AT_CHECK([ovs-vsctl add-port br0 p1 -- set Interface p1 type=dummy-pmd ofport_request=1 options:n_rxq=1 options:pstream=punix:$OVS_RUNDIR/net.sock])
AT_CHECK([ovs-vsctl add-port br0 p2 -- set Interface p2 type=dummy-pmd ofport_request=2 options:n_rxq=1 options:stream=unix:$OVS_RUNDIR/net.sock])

AT_CHECK([ovs-appctl dpif-netdev/pmd-rxq-show | parse_pmd_rxq_show], [0], [dnl
p1 0 0 0
p2 0 0 0
])

dnl Enable bfd with a very aggressive interval. This will make the monitor very
dnl busy, and uncover race conditions with the main thread.
AT_CHECK([ovs-vsctl set Interface p1 bfd:enable=true bfd:min_rx=1 bfd:min_tx=1])
AT_CHECK([ovs-vsctl set Interface p2 bfd:enable=true bfd:min_rx=1 bfd:min_tx=1])

AT_CHECK([ovs-vsctl --timeout=10 wait-until Interface p1 bfd_status:forwarding=true \
-- wait-until Interface p2 bfd_status:forwarding=true])

dnl Trigger reconfiguration of the datapath
AT_CHECK([ovs-vsctl set Interface p1 options:n_rxq=2])
AT_CHECK([ovs-vsctl set Interface p2 options:n_rxq=2])

dnl Make sure that reconfiguration succeded
AT_CHECK([ovs-appctl dpif-netdev/pmd-rxq-show | parse_pmd_rxq_show], [0], [dnl
p1 0 0 0
p1 1 0 0
p2 0 0 0
p2 1 0 0
])

dnl During reconfiguration some packets will be dropped. This is expected
OVS_VSWITCHD_STOP(["/dpif(monitor[[0-9]]\+)|WARN|dummy@ovs-dummy: execute [[0-9]]\+ failed/d"])
AT_CLEANUP

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