hastd: assertion (res->hr_event != NULL) fails in secondary on split-brain

[Mikolaj Golub]

Hi,

After recent changes in hastd (I think r213006: Fix descriptor leaks) if
split-brain occurs hastd will abort in child_cleanup() on assertion
(res->hr_event != NULL).

Oct  2 17:24:17 lolek hastd[39334]: [storage] (init) Role changed to secondary.
Oct  2 17:24:17 lolek hastd[39334]: Accepting connection to tcp4://0.0.0.0:8457.
Oct  2 17:24:17 lolek hastd[39334]: Connection from tcp4://172.20.68.12:17367 to tcp4://172.20.68.11:8457.
Oct  2 17:24:17 lolek hastd[39334]: tcp4://172.20.68.12:17367: resource=storage
Oct  2 17:24:17 lolek hastd[39334]: [storage] (secondary) Initial connection from tcp4://172.20.68.12:17367.
Oct  2 17:24:17 lolek hastd[39334]: [storage] (secondary) Incoming connection from tcp4://172.20.68.12:17367 configured.
Oct  2 17:24:17 lolek hastd[39334]: Accepting connection to tcp4://0.0.0.0:8457.
Oct  2 17:24:17 lolek hastd[39334]: Connection from tcp4://172.20.68.12:13769 to tcp4://172.20.68.11:8457.
Oct  2 17:24:17 lolek hastd[39334]: tcp4://172.20.68.12:13769: resource=storage
Oct  2 17:24:17 lolek hastd[39334]: [storage] (secondary) Outgoing connection to tcp4://172.20.68.12:13769 configured.
Oct  2 17:24:17 lolek hastd[39339]: [storage] (secondary) Obtained info about /dev/ad4.
Oct  2 17:24:17 lolek hastd[39339]: [storage] (secondary) Locked /dev/ad4.
Oct  2 17:24:17 lolek hastd[39339]: [storage] (secondary) Split-brain detected, exiting.
Oct  2 17:24:17 lolek hastd[39334]: Unable to receive event header: Socket is not connected.
Oct  2 17:24:28 lolek hastd[39334]: Accepting connection to tcp4://0.0.0.0:8457.
Oct  2 17:24:28 lolek hastd[39334]: Connection from tcp4://172.20.68.12:59760 to tcp4://172.20.68.11:8457.
Oct  2 17:24:28 lolek hastd[39334]: tcp4://172.20.68.12:59760: resource=storage
Oct  2 17:24:28 lolek hastd[39334]: [storage] (secondary) Initial connection from tcp4://172.20.68.12:59760.
Oct  2 17:24:28 lolek hastd[39334]: [storage] (secondary) Worker process exists (pid=39339), stopping it.
Oct  2 17:24:28 lolek hastd[39334]: [storage] (secondary) Worker process exited ungracefully (pid=39339, exitcode=78).
Oct  2 17:24:28 lolek kernel: pid 39334 (hastd), uid 0: exited on signal 6 (core dumped)

(gdb) bt
#0  0x28348d87 in kill () from /lib/libc.so.7
#1  0x280e1017 in raise () from /lib/libthr.so.3
#2  0x2834787a in abort () from /lib/libc.so.7
#3  0x2832fc86 in __assert () from /lib/libc.so.7
#4  0x0805f300 in proto_close (conn=0x0) at /usr/src/sbin/hastd/proto.c:287
#5  0x0804c445 in child_cleanup (res=0x284eb500) at /usr/src/sbin/hastd/control.c:61
#6  0x0804fc6d in listen_accept () at /usr/src/sbin/hastd/hastd.c:526
#7  0x0805059a in main_loop () at /usr/src/sbin/hastd/hastd.c:673
#8  0x08050a7f in main (argc=0, argv=0xbfbfed80) at /usr/src/sbin/hastd/hastd.c:784
(gdb) fr 5
#5  0x0804c445 in child_cleanup (res=0x284eb500) at /usr/src/sbin/hastd/control.c:61
61              proto_close(res->hr_event);
(gdb) list
56      child_cleanup(struct hast_resource *res)
57      {
58
59              proto_close(res->hr_ctrl);
60              res->hr_ctrl = NULL;
61              proto_close(res->hr_event);
62              res->hr_event = NULL;
63              res->hr_workerpid = 0;
64      }
65

So we have double close of res->hr_event. The first time it is closed when
parent detects that worker exited in main_loop(), and the second time when a
new connection from primary comes and the parent does cleanup after previously
terminated child before starting new one.

The straightforward fix is to check res->hr_event before closing, like in the
patch below.

-- 
Mikolaj Golub

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