Github user shinrich commented on the issue:
https://github.com/apache/trafficserver/issues/1401
I've finally got my environment running and I see the same stack very
quickly as well. In the cases I've seen it looks like there was a write error,
but for some reason the write vio has been cleared out (or was never set?)
```
(gdb) frame 2
#2 0x0000000000788350 in write_to_net_io (nh=0x2af588003e60,
vc=0x2aad1401b800, thread=0x2af588000010) at UnixNetVConnection.cc:440
440 UnixNetVConnection.cc: No such file or directory.
in UnixNetVConnection.cc
(gdb) print *s
$1 = {enabled = 0, error = 1, vio = {_cont = 0x0, nbytes = 0, ndone = 0, op
= 0, buffer = {mbuf = 0x0, entry = 0x0}, vc_server = 0x0, mutex = {m_ptr =
0x0}},
ready_link = {<SLink<UnixNetVConnection>> = {next = 0x0}, prev = 0x0},
enable_link = {next = 0x0}, in_enabled_list = 0, triggered = 1}
```
The write.error stuff was added by Thomas in TS-4796, but if this just
showed up between 7.0 and 7.1, it is unlikely that this was the culprit. I
think it has been a while (since 9/3/2016).
Seems more likely that someone has cleared the vio, or we are bouncing an
error.
In the short term I'm adding a NULL check at the begining of
write_to_net_io, but that just seems to be masking the failure case rather than
identifying the root cause.
```
+ if (!s->vio.mutex) {
+ ink_release_assert(s->vio._cont == NULL && vc->write.error);
+ return;
+ }
```
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