chan_pjsip: Fix deadlock when masquerading PJSIP channels.

Performing a directed call pickup resulted in a deadlock when PJSIP
channels were involved.

A masquerade needs to hold onto the channel locks while it swaps channel
information between the two channels involved in the masquerade.  With
PJSIP channels, the fixup routine needed to push a fixup task onto the
PJSIP channel's serializer.  Unfortunately, if the serializer was also
processing a task that needed to lock the channel, you get deadlock.

* Added a new control frame that is used to notify the channels that a
masquerade is about to start and when it has completed.

* Added the ability to query taskprocessors if the current thread is the
taskprocessor thread.

* Added the ability to suspend/unsuspend the PJSIP serializer thread so a
masquerade could fixup the PJSIP channel without using the serializer.

ASTERISK-24356 #close
Reported by: rmudgett

Review: https://reviewboard.asterisk.org/r/4034/
........

Merged revisions 424471 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/13@424472 65c4cc65-6c06-0410-ace0-fbb531ad65f3

3 files changed, 57 insertions, 19 deletions

diff --git a/include/asterisk/frame.h b/include/asterisk/frame.h
index a981c7e72..20f40f863 100644
--- a/include/asterisk/frame.h
+++ b/include/asterisk/frame.h
@@ -290,6 +290,7 @@ enum ast_control_frame_type {
 	AST_CONTROL_MCID = 31,			/*!< Indicate that the caller is being malicious. */
 	AST_CONTROL_UPDATE_RTP_PEER = 32, /*!< Interrupt the bridge and have it update the peer */
 	AST_CONTROL_PVT_CAUSE_CODE = 33, /*!< Contains an update to the protocol-specific cause-code stored for branching dials */
+	AST_CONTROL_MASQUERADE_NOTIFY = 34,	/*!< A masquerade is about to begin/end. (Never sent as a frame but directly with ast_indicate_data().) */
 
 	/*
 	 * WARNING WARNING WARNING WARNING WARNING WARNING WARNING WARNING WARNING
diff --git a/include/asterisk/res_pjsip_session.h b/include/asterisk/res_pjsip_session.h
index 010a74dc0..3344a6b38 100644
--- a/include/asterisk/res_pjsip_session.h
+++ b/include/asterisk/res_pjsip_session.h
@@ -87,6 +87,9 @@ struct ast_sip_session_media {
  */
 struct ast_sip_session_delayed_request;
 
+/*! \brief Opaque struct controlling the suspension of the session's serializer. */
+struct ast_sip_session_suspender;
+
 /*!
  * \brief A structure describing a SIP session
  *
@@ -96,43 +99,45 @@ struct ast_sip_session_delayed_request;
  * to use the term "SIP session" to refer to the INVITE dialog itself.
  */
 struct ast_sip_session {
-	/* Dialplan extension where incoming call is destined */
+	/*! Dialplan extension where incoming call is destined */
 	char exten[AST_MAX_EXTENSION];
-	/* The endpoint with which Asterisk is communicating */
+	/*! The endpoint with which Asterisk is communicating */
 	struct ast_sip_endpoint *endpoint;
-	/* The contact associated with this session */
+	/*! The contact associated with this session */
 	struct ast_sip_contact *contact;
-	/* The PJSIP details of the session, which includes the dialog */
+	/*! The PJSIP details of the session, which includes the dialog */
 	struct pjsip_inv_session *inv_session;
-	/* The Asterisk channel associated with the session */
+	/*! The Asterisk channel associated with the session */
 	struct ast_channel *channel;
-	/* Registered session supplements */
+	/*! Registered session supplements */
 	AST_LIST_HEAD(, ast_sip_session_supplement) supplements;
-	/* Datastores added to the session by supplements to the session */
+	/*! Datastores added to the session by supplements to the session */
 	struct ao2_container *datastores;
-	/* Media streams */
+	/*! Media streams */
 	struct ao2_container *media;
-	/* Serializer for tasks relating to this SIP session */
+	/*! Serializer for tasks relating to this SIP session */
 	struct ast_taskprocessor *serializer;
-	/* Requests that could not be sent due to current inv_session state */
+	/*! Non-null if the session serializer is suspended or being suspended. */
+	struct ast_sip_session_suspender *suspended;
+	/*! Requests that could not be sent due to current inv_session state */
 	AST_LIST_HEAD_NOLOCK(, ast_sip_session_delayed_request) delayed_requests;
-	/* When we need to reschedule a reinvite, we use this structure to do it */
+	/*! When we need to reschedule a reinvite, we use this structure to do it */
 	pj_timer_entry rescheduled_reinvite;
-	/* Format capabilities pertaining to direct media */
+	/*! Format capabilities pertaining to direct media */
 	struct ast_format_cap *direct_media_cap;
-	/* When we need to forcefully end the session */
+	/*! When we need to forcefully end the session */
 	pj_timer_entry scheduled_termination;
-	/* Identity of endpoint this session deals with */
+	/*! Identity of endpoint this session deals with */
 	struct ast_party_id id;
-	/* Requested capabilities */
+	/*! Requested capabilities */
 	struct ast_format_cap *req_caps;
-	/* Optional DSP, used only for inband DTMF detection if configured */
+	/*! Optional DSP, used only for inband DTMF detection if configured */
 	struct ast_dsp *dsp;
-	/* Whether the termination of the session should be deferred */
+	/*! Whether the termination of the session should be deferred */
 	unsigned int defer_terminate:1;
-	/* Deferred incoming re-invite */
+	/*! Deferred incoming re-invite */
 	pjsip_rx_data *deferred_reinvite;
-	/* Current T.38 state */
+	/*! Current T.38 state */
 	enum ast_sip_session_t38state t38state;
 };
 
@@ -388,6 +393,28 @@ struct ast_sip_session *ast_sip_session_alloc(struct ast_sip_endpoint *endpoint,
 	struct ast_sip_contact *contact, pjsip_inv_session *inv);
 
 /*!
+ * \brief Request and wait for the session serializer to be suspended.
+ * \since 12.7.0
+ *
+ * \param session Which session to suspend the serializer.
+ *
+ * \note No channel locks can be held while calling without risk of deadlock.
+ *
+ * \return Nothing
+ */
+void ast_sip_session_suspend(struct ast_sip_session *session);
+
+/*!
+ * \brief Request the session serializer be unsuspended.
+ * \since 12.7.0
+ *
+ * \param session Which session to unsuspend the serializer.
+ *
+ * \return Nothing
+ */
+void ast_sip_session_unsuspend(struct ast_sip_session *session);
+
+/*!
  * \brief Create a new outgoing SIP session
  *
  * The endpoint that is passed in will have its reference count increased by one since
diff --git a/include/asterisk/taskprocessor.h b/include/asterisk/taskprocessor.h
index ab523290c..f16f144cb 100644
--- a/include/asterisk/taskprocessor.h
+++ b/include/asterisk/taskprocessor.h
@@ -247,6 +247,16 @@ int ast_taskprocessor_push_local(struct ast_taskprocessor *tps,
 int ast_taskprocessor_execute(struct ast_taskprocessor *tps);
 
 /*!
+ * \brief Am I the given taskprocessor's current task.
+ * \since 12.7.0
+ *
+ * \param tps Taskprocessor to check.
+ *
+ * \retval non-zero if current thread is the taskprocessor thread.
+ */
+int ast_taskprocessor_is_task(struct ast_taskprocessor *tps);
+
+/*!
  * \brief Return the name of the taskprocessor singleton
  * \since 1.6.1
  */