Major Description
We've noticed a few crashes for requests using SPDY (on ATS 5.2.x and 6..x) where the downstream origin is down with a backtrace that looks something like:
(gdb) bt #0 0x0000000000000000 in ?? () #1 0x00000000004cfe54 in set_continuation (this=0x2afe63a93530, event=1, edata=0x2afe6399fc40) at ../iocore/eventsystem/P_VIO.h:104 #2 INKVConnInternal::handle_event (this=0x2afe63a93530, event=1, edata=0x2afe6399fc40) at InkAPI.cc:1060 #3 0x00000000006f8e65 in handleEvent (this=0x2afe3dd07000, e=0x2afe6399fc40, calling_code=1) at I_Continuation.h:146 #4 EThread::process_event (this=0x2afe3dd07000, e=0x2afe6399fc40, calling_code=1) at UnixEThread.cc:144 #5 0x00000000006f993b in EThread::execute (this=0x2afe3dd07000) at UnixEThread.cc:195 #6 0x00000000006f832a in spawn_thread_internal (a=0x2afe3badf400) at Thread.cc:88 #7 0x0000003861c079d1 in start_thread () from /lib64/libpthread.so.0 #8 0x00000038614e8b5d in clone () from /lib64/libc.so.6
Which looks a bit odd-- as frame 0 is missing. From digging into it a bit more (with the help of amc) we found that the VC we where calling was an INKContInternal (meaning an INKVConnInternal):
(gdb) p (INKVConnInternal) *vc_server
$5 = {<INKContInternal> = {<DummyVConnection> = {<VConnection> = {<Continuation> = {<force_VFPT_to_top> = {_vptr.force_VFPT_to_top = 0x2afe63a93170},
handler = (int (Continuation::*)(Continuation *, int,
void *)) 0x4cfd90 <INKVConnInternal::handle_event(int, void*)>, mutex = {
m_ptr = 0x0}, link = {<SLink<Continuation>> = {next = 0x0},
prev = 0x0}}, lerrno = 20600}, <No data fields>},
mdata = 0xdeaddead, m_event_func = 0x2afe43c18490
<(anonymous namespace)::handleTransformationPluginEvents(TSCont, TSEvent, void*)>, m_event_count = 0, m_closed = -1, m_deletable = 1, m_deleted = 1,
m_free_magic = INKCONT_INTERN_MAGIC_ALIVE}, m_read_vio = {_cont = 0x0,
nbytes = 0, ndone = 0, op = 0, buffer = {mbuf = 0x0, entry = 0x0},
vc_server = 0x0, mutex = {m_ptr = 0x0}}, m_write_vio = {_cont = 0x0,
nbytes = 122, ndone = 0, op = 0, buffer = {mbuf = 0x0, entry = 0x0},
vc_server = 0x2afe63a93530, mutex = {m_ptr = 0x0}},
m_output_vc = 0x2afe63091a88}
From looking at the debug logs that lead up to the crash, I'm seeing that some events (namely timeout events) are being called after the VConn has been destroy()'d . This lead me to find that INKVConnInternal::handle_event is actually checking if that is the case-- and then re-destroying everything, which makes no sense.
So although the ideal would be to not call handle_event on a closed VConn, crashing is definitely not acceptable. My solution is to continue to only call the event handler if the VConn hasn't been deleted-- but instead of attempting to re-destroy the connection, we'll leave it be (unless we are in debug mode-- where I'll throw in an assert).
I did some looking at this on ATS7 and it looks like this is all fixed by the cleanup of the whole free-ing stuff for VConns (https://github.com/apache/trafficserver/pull/752/files).
