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stasis/control: Fix possible deadlock with swap channel 

If an error occurs during a bridge impart it's possible that
the "bridge_after" callback might try to run before
control_swap_channel_in_bridge has been signalled to continue.
Since control_swap_channel_in_bridge is holding the control lock
and the callback needs it, a deadlock will occur.

* control_swap_channel_in_bridge now only holds the control
  lock while it's actually modifying the control structure and
  releases it while the bridge impart is running.
* bridge_after_cb is now tolerant of impart failures.

Change-Id: Ifd239aa93955b3eb475521f61e284fcb0da2c3b3
This commit is contained in:
George Joseph 2017-09-01 04:17:02 -06:00 committed by Richard Mudgett
parent 2857a3334a
commit 94091c7b96
4 changed files with 96 additions and 64 deletions
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2
include/asterisk/bridge_after.h
View File

@ -45,6 +45,8 @@ enum ast_bridge_after_cb_reason {
AST_BRIDGE_AFTER_CB_REASON_DEPART,
/*! Was explicitly removed by external code. */
AST_BRIDGE_AFTER_CB_REASON_REMOVED,
/*! The channel failed to enter the bridge. */
AST_BRIDGE_AFTER_CB_REASON_IMPART_FAILED,
};
/*!

6
main/bridge.c
View File

@ -1758,12 +1758,13 @@ join_exit:;
static void *bridge_channel_depart_thread(void *data)
{
struct ast_bridge_channel *bridge_channel = data;
int res = 0;
if (bridge_channel->callid) {
ast_callid_threadassoc_add(bridge_channel->callid);
}
bridge_channel_internal_join(bridge_channel);
res = bridge_channel_internal_join(bridge_channel);
/*
* cleanup
@ -1775,7 +1776,8 @@ static void *bridge_channel_depart_thread(void *data)
ast_bridge_features_destroy(bridge_channel->features);
bridge_channel->features = NULL;
ast_bridge_discard_after_callback(bridge_channel->chan, AST_BRIDGE_AFTER_CB_REASON_DEPART);
ast_bridge_discard_after_callback(bridge_channel->chan,
res ? AST_BRIDGE_AFTER_CB_REASON_IMPART_FAILED : AST_BRIDGE_AFTER_CB_REASON_DEPART);
/* If join failed there will be impart threads waiting. */
bridge_channel_impart_signal(bridge_channel->chan);
ast_bridge_discard_after_goto(bridge_channel->chan);

28
main/bridge_after.c
View File

@ -293,23 +293,23 @@ int ast_bridge_set_after_callback(struct ast_channel *chan, ast_bridge_after_cb
return 0;
}
const char *reason_strings[] = {
[AST_BRIDGE_AFTER_CB_REASON_DESTROY] = "Channel destroyed (hungup)",
[AST_BRIDGE_AFTER_CB_REASON_REPLACED] = "Callback was replaced",
[AST_BRIDGE_AFTER_CB_REASON_MASQUERADE] = "Channel masqueraded",
[AST_BRIDGE_AFTER_CB_REASON_DEPART] = "Channel was departed from bridge",
[AST_BRIDGE_AFTER_CB_REASON_REMOVED] = "Callback was removed",
};
const char *ast_bridge_after_cb_reason_string(enum ast_bridge_after_cb_reason reason)
{
if (reason < AST_BRIDGE_AFTER_CB_REASON_DESTROY
|| AST_BRIDGE_AFTER_CB_REASON_REMOVED < reason
|| !reason_strings[reason]) {
return "Unknown";
switch (reason) {
case AST_BRIDGE_AFTER_CB_REASON_DESTROY:
return "Channel destroyed (hungup)";
case AST_BRIDGE_AFTER_CB_REASON_REPLACED:
return "Callback was replaced";
case AST_BRIDGE_AFTER_CB_REASON_MASQUERADE:
return "Channel masqueraded";
case AST_BRIDGE_AFTER_CB_REASON_DEPART:
return "Channel was departed from bridge";
case AST_BRIDGE_AFTER_CB_REASON_REMOVED:
return "Callback was removed";
case AST_BRIDGE_AFTER_CB_REASON_IMPART_FAILED:
return "Channel failed joining the bridge";
}
return reason_strings[reason];
return "Unknown";
}
struct after_bridge_goto_ds {

124
res/stasis/control.c
View File

@ -983,14 +983,21 @@ static int bridge_channel_depart(struct stasis_app_control *control,
return 0;
}
static void bridge_after_cb(struct ast_channel *chan, void *data)
static void internal_bridge_after_cb(struct ast_channel *chan, void *data,
enum ast_bridge_after_cb_reason reason)
{
struct stasis_app_control *control = data;
SCOPED_AO2LOCK(lock, control);
struct ast_bridge_channel *bridge_channel;
ast_debug(3, "%s, %s: Channel leaving bridge\n",
ast_channel_uniqueid(chan), control->bridge->uniqueid);
ast_debug(3, "%s, %s: %s\n",
ast_channel_uniqueid(chan), control->bridge ? control->bridge->uniqueid : "unknown",
ast_bridge_after_cb_reason_string(reason));
if (reason == AST_BRIDGE_AFTER_CB_REASON_IMPART_FAILED) {
/* The impart actually failed so control->bridge isn't valid. */
control->bridge = NULL;
}
ast_assert(chan == control->channel);
@ -998,18 +1005,21 @@ static void bridge_after_cb(struct ast_channel *chan, void *data)
ast_channel_pbx_set(control->channel, control->pbx);
control->pbx = NULL;
app_unsubscribe_bridge(control->app, control->bridge);
if (control->bridge) {
app_unsubscribe_bridge(control->app, control->bridge);
/* No longer in the bridge */
control->bridge = NULL;
/* No longer in the bridge */
control->bridge = NULL;
/* Get the bridge channel so we don't depart from the wrong bridge */
ast_channel_lock(chan);
bridge_channel = ast_channel_get_bridge_channel(chan);
ast_channel_unlock(chan);
/* Get the bridge channel so we don't depart from the wrong bridge */
ast_channel_lock(chan);
bridge_channel = ast_channel_get_bridge_channel(chan);
ast_channel_unlock(chan);
/* Depart this channel from the bridge using the command queue if possible */
stasis_app_send_command_async(control, bridge_channel_depart, bridge_channel, __ao2_cleanup);
}
/* Depart this channel from the bridge using the command queue if possible */
stasis_app_send_command_async(control, bridge_channel_depart, bridge_channel, __ao2_cleanup);
if (stasis_app_channel_is_stasis_end_published(chan)) {
/* The channel has had a StasisEnd published on it, but until now had remained in
* the bridging system. This means that the channel moved from a Stasis bridge to a
@ -1027,12 +1037,19 @@ static void bridge_after_cb(struct ast_channel *chan, void *data)
}
}
static void bridge_after_cb(struct ast_channel *chan, void *data)
{
struct stasis_app_control *control = data;
internal_bridge_after_cb(control->channel, data, AST_BRIDGE_AFTER_CB_REASON_DEPART);
}
static void bridge_after_cb_failed(enum ast_bridge_after_cb_reason reason,
void *data)
{
struct stasis_app_control *control = data;
bridge_after_cb(control->channel, data);
internal_bridge_after_cb(control->channel, data, reason);
ast_debug(3, " reason: %s\n",
ast_bridge_after_cb_reason_string(reason));
@ -1171,46 +1188,57 @@ int control_swap_channel_in_bridge(struct stasis_app_control *control, struct as
return -1;
}
{
/* pbx and bridge are modified by the bridging impart thread.
* It shouldn't happen concurrently, but we still need to lock
* for the memory fence.
ao2_lock(control);
/* Ensure the controlling application is subscribed early enough
* to receive the ChannelEnteredBridge message. This works in concert
* with the subscription handled in the Stasis application execution
* loop */
app_subscribe_bridge(control->app, bridge);
/* Save off the channel's PBX */
ast_assert(control->pbx == NULL);
if (!control->pbx) {
control->pbx = ast_channel_pbx(chan);
ast_channel_pbx_set(chan, NULL);
}
ast_assert(stasis_app_get_bridge(control) == NULL);
/* We need to set control->bridge here since bridge_after_cb may be run
* before ast_bridge_impart returns. bridge_after_cb gets a reason
* code so it can tell if the bridge is actually valid or not.
*/
control->bridge = bridge;
/* We can't be holding the control lock while impart is running
* or we could create a deadlock with bridge_after_cb which also
* tries to lock control.
*/
ao2_unlock(control);
res = ast_bridge_impart(bridge,
chan,
swap,
NULL, /* features */
AST_BRIDGE_IMPART_CHAN_DEPARTABLE);
if (res != 0) {
/* ast_bridge_impart failed before it could spawn the depart
* thread. The callbacks aren't called in this case.
* The impart could still fail even if ast_bridge_impart returned
* ok but that's handled by bridge_after_cb.
*/
SCOPED_AO2LOCK(lock, control);
/* Ensure the controlling application is subscribed early enough
* to receive the ChannelEnteredBridge message. This works in concert
* with the subscription handled in the Stasis application execution
* loop */
app_subscribe_bridge(control->app, bridge);
/* Save off the channel's PBX */
ast_assert(control->pbx == NULL);
if (!control->pbx) {
control->pbx = ast_channel_pbx(chan);
ast_channel_pbx_set(chan, NULL);
}
res = ast_bridge_impart(bridge,
chan,
swap,
NULL, /* features */
AST_BRIDGE_IMPART_CHAN_DEPARTABLE);
if (res != 0) {
ast_log(LOG_ERROR, "Error adding channel to bridge\n");
ast_channel_pbx_set(chan, control->pbx);
control->pbx = NULL;
return -1;
}
ast_assert(stasis_app_get_bridge(control) == NULL);
control->bridge = bridge;
ast_log(LOG_ERROR, "Error adding channel to bridge\n");
ao2_lock(control);
ast_channel_pbx_set(chan, control->pbx);
control->pbx = NULL;
control->bridge = NULL;
ao2_unlock(control);
} else {
ast_channel_lock(chan);
set_interval_hook(chan);
ast_channel_unlock(chan);
}
return 0;
return res;
}
int control_add_channel_to_bridge(struct stasis_app_control *control, struct ast_channel *chan, void *data)