Github user jacksontj commented on the issue:
https://github.com/apache/trafficserver/pull/947
After doing some testing with this patch, I see crashes where write_to_net
is being called with a null vc lock.
```
(gdb) list
416 }
417 while ((vc = write_ready_list.dequeue())) {
418 if (vc->closed)
419 close_UnixNetVConnection(vc, trigger_event->ethread);
420 else if ((vc->write.enabled && vc->write.triggered) ||
vc->write.error)
421 write_to_net(this, vc, trigger_event->ethread);
422 else if (!vc->write.enabled) {
423 write_ready_list.remove(vc);
```
Seems that vc->write.error forces write_to_net to be called, but nothing is
checking that the vc is non-null.
Specifically:
```
(gdb) p lock
$1 = {m = {m_ptr = 0x0}, lock_acquired = 157}
(gdb) list
382 write_to_net_io(NetHandler *nh, UnixNetVConnection *vc, EThread *thread)
383 {
384 NetState *s = &vc->write;
385 ProxyMutex *mutex = thread->mutex;
386
387 MUTEX_TRY_LOCK_FOR(lock, s->vio.mutex, thread, s->vio._cont); // <--
this line, specifically the s->vio.mutex
388
389 if (!lock.is_locked() || lock.get_mutex() != s->vio.mutex.m_ptr) {
390 write_reschedule(nh, vc);
391 return;
```
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