Better way to get chan and pvt lock for issue ASTERISK-17431.

Redoes -r308945 for issue ASTERISK-17431 deadlock fix for
sip_set_udptl_peer() and sip_set_rtp_peer().

* Lock the channels in the defined order and avoid the need for a deadlock
avoidance loop.

* Lock the channel before getting the pointer to the private structure to
be sure that the pointer will not change due to a masquerade or channel
hangup.

* To preserve sanity, check that chan and p->owner are the same.  (Pointer
rearangements should not happen without the protection of locks because
bad things tend to happen otherwise.)

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.8@326144 65c4cc65-6c06-0410-ace0-fbb531ad65f3

diff --git a/channels/chan_sip.c b/channels/chan_sip.c
index 077d84efe5c39a490286ca5f9b14ceaf7484d9c7..f1a35a4d596baf6e7fe4c4bacc211e6475511036 100644 (file)
--- a/channels/chan_sip.c
+++ b/channels/chan_sip.c
@@ -28087,25 +28087,23 @@ static struct ast_udptl *sip_get_udptl_peer(struct ast_channel *chan)
 static int sip_set_udptl_peer(struct ast_channel *chan, struct ast_udptl *udptl)
 {
        struct sip_pvt *p;
-       
+
+       /* Lock the channel and the private safely. */
+       ast_channel_lock(chan);
        p = chan->tech_pvt;
        if (!p) {
+               ast_channel_unlock(chan);
                return -1;
        }
-       /*
-        * Lock both the pvt and it's owner safely.
-        */
        sip_pvt_lock(p);
-       while (p->owner && ast_channel_trylock(p->owner)) {
-               sip_pvt_unlock(p);
-               usleep(1);
-               sip_pvt_lock(p);
-       }
-
-       if (!p->owner) {
+       if (p->owner != chan) {
+               /* I suppose it could be argued that if this happens it is a bug. */
+               ast_debug(1, "The private is not owned by channel %s anymore.\n", chan->name);
                sip_pvt_unlock(p);
+               ast_channel_unlock(chan);
                return 0;
        }
+
        if (udptl) {
                ast_udptl_get_peer(udptl, &p->udptlredirip);
        } else {
@@ -28124,8 +28122,8 @@ static int sip_set_udptl_peer(struct ast_channel *chan, struct ast_udptl *udptl)
        }
        /* Reset lastrtprx timer */
        p->lastrtprx = p->lastrtptx = time(NULL);
-       ast_channel_unlock(p->owner);
        sip_pvt_unlock(p);
+       ast_channel_unlock(chan);
        return 0;
 }
 
@@ -28232,10 +28230,21 @@ static int sip_set_rtp_peer(struct ast_channel *chan, struct ast_rtp_instance *i
        struct sip_pvt *p;
        int changed = 0;
 
+       /* Lock the channel and the private safely. */
+       ast_channel_lock(chan);
        p = chan->tech_pvt;
        if (!p) {
+               ast_channel_unlock(chan);
                return -1;
        }
+       sip_pvt_lock(p);
+       if (p->owner != chan) {
+               /* I suppose it could be argued that if this happens it is a bug. */
+               ast_debug(1, "The private is not owned by channel %s anymore.\n", chan->name);
+               sip_pvt_unlock(p);
+               ast_channel_unlock(chan);
+               return 0;
+       }
 
        /* Disable early RTP bridge  */
        if ((instance || vinstance || tinstance) &&
@@ -28244,25 +28253,10 @@ static int sip_set_rtp_peer(struct ast_channel *chan, struct ast_rtp_instance *i
                        return 0;
        }
 
-       /*
-        * Lock both the pvt and it's owner safely.
-        */
-       sip_pvt_lock(p);
-       while (p->owner && ast_channel_trylock(p->owner)) {
-               sip_pvt_unlock(p);
-               usleep(1);
-               sip_pvt_lock(p);
-       }
-
-       if (!p->owner) {
-               sip_pvt_unlock(p);
-               return 0;
-       }
-
        if (p->alreadygone) {
                /* If we're destroyed, don't bother */
-               ast_channel_unlock(p->owner);
                sip_pvt_unlock(p);
+               ast_channel_unlock(chan);
                return 0;
        }
 
@@ -28270,8 +28264,8 @@ static int sip_set_rtp_peer(struct ast_channel *chan, struct ast_rtp_instance *i
           that are known to be behind a NAT, then stop the process now
        */
        if (nat_active && !ast_test_flag(&p->flags[0], SIP_DIRECT_MEDIA_NAT)) {
-               ast_channel_unlock(p->owner);
                sip_pvt_unlock(p);
+               ast_channel_unlock(chan);
                return 0;
        }
 
@@ -28313,8 +28307,8 @@ static int sip_set_rtp_peer(struct ast_channel *chan, struct ast_rtp_instance *i
        }
        /* Reset lastrtprx timer */
        p->lastrtprx = p->lastrtptx = time(NULL);
-       ast_channel_unlock(p->owner);
        sip_pvt_unlock(p);
+       ast_channel_unlock(chan);
        return 0;
 }