Use-after-free in client on connection loss

[redlicha]

Observed while working on #8 , not trivially reproducible so far:

==16470==ERROR: AddressSanitizer: heap-use-after-free on address 0x614000230098 at pc 0x7f67470504e1 bp 0x7f66a861a950 sp 0x7f66a861a948
READ of size 8 at 0x614000230098 thread T91 (xio_event_loop)
    #0 0x7f67470504e0 in xio_observable_notify_all_observers /home/jenkins/openvstorage/accelio/git/src/usr/../common/xio_observer.c:219:2
    #1 0x7f6747083602 in xio_nexus_disconnected /home/jenkins/openvstorage/accelio/git/src/usr/../common/xio_nexus.c:1425:3
    #2 0x7f6747076546 in xio_nexus_on_transport_disconnected /home/jenkins/openvstorage/accelio/git/src/usr/../common/xio_nexus.c:1467:2
    #3 0x7f6747058216 in xio_nexus_on_transport_event /home/jenkins/openvstorage/accelio/git/src/usr/../common/xio_nexus.c:1695:3
    #4 0x7f67470503e2 in xio_observable_notify_all_observers /home/jenkins/openvstorage/accelio/git/src/usr/../common/xio_observer.c:223:4
    #5 0x7f6746f3fc3c in xio_transport_notify_observer /home/jenkins/openvstorage/accelio/git/src/common/xio_transport.h:305:2
    #6 0x7f6746f3f5aa in on_sock_disconnected /home/jenkins/openvstorage/accelio/git/src/usr/transport/tcp/xio_tcp_management.c:278:4
    #7 0x7f6746f46291 in xio_tcp_disconnect_handler /home/jenkins/openvstorage/accelio/git/src/usr/transport/tcp/xio_tcp_management.c:521:2
    #8 0x7f6746e319f3 in xio_ev_loop_exec_scheduled /home/jenkins/openvstorage/accelio/git/src/usr/xio/xio_ev_loop.c:368:4
    #9 0x7f6746e2ceba in xio_ev_loop_run_helper /home/jenkins/openvstorage/accelio/git/src/usr/xio/xio_ev_loop.c:412:17
    #10 0x7f6746e2ee79 in xio_ev_loop_run /home/jenkins/openvstorage/accelio/git/src/usr/xio/xio_ev_loop.c:514:9
    #11 0x7f6746e4f1eb in xio_context_run_loop /home/jenkins/openvstorage/accelio/git/src/usr/xio/xio_context.c:504:42
    [...]

0x614000230098 is located 88 bytes inside of 432-byte region [0x614000230040,0x6140002301f0)
freed by thread T91 (xio_event_loop) here:
[...]
    #1 0x7f6747085315 in ufree /home/jenkins/openvstorage/accelio/git/src/usr/xio/xio_mem.h:119:3
    #2 0x7f6747065774 in kfree /home/jenkins/openvstorage/accelio/git/src/usr/linux/slab.h:19:2
    #3 0x7f674705e569 in xio_nexus_destroy /home/jenkins/openvstorage/accelio/git/src/usr/../common/xio_nexus.c:1801:2
    #4 0x7f6747076568 in xio_nexus_on_transport_closed /home/jenkins/openvstorage/accelio/git/src/usr/../common/xio_nexus.c:1343:2
    #5 0x7f6747058348 in xio_nexus_on_transport_event /home/jenkins/openvstorage/accelio/git/src/usr/../common/xio_nexus.c:1701:3
    #6 0x7f67470503e2 in xio_observable_notify_all_observers /home/jenkins/openvstorage/accelio/git/src/usr/../common/xio_observer.c:223:4
    #7 0x7f6746f3fc3c in xio_transport_notify_observer /home/jenkins/openvstorage/accelio/git/src/common/xio_transport.h:305:2
    #8 0x7f6746f67331 in on_sock_close /home/jenkins/openvstorage/accelio/git/src/usr/transport/tcp/xio_tcp_management.c:171:2
    #9 0x7f6746f66c08 in xio_tcp_close_cb /home/jenkins/openvstorage/accelio/git/src/usr/transport/tcp/xio_tcp_management.c:335:3
    #10 0x7f6746f66f1a in kref_sub /home/jenkins/openvstorage/accelio/git/src/usr/linux/kref.h:73:3
    #11 0x7f6746f66791 in kref_put /home/jenkins/openvstorage/accelio/git/src/usr/linux/kref.h:98:9
    #12 0x7f6746f61ef9 in xio_tcp_close /home/jenkins/openvstorage/accelio/git/src/usr/transport/tcp/xio_tcp_management.c:369:2
    #13 0x7f674706f2aa in xio_nexus_release_cb /home/jenkins/openvstorage/accelio/git/src/usr/../common/xio_nexus.c:1095:3
    #14 0x7f674706e87f in xio_nexus_release /home/jenkins/openvstorage/accelio/git/src/usr/../common/xio_nexus.c:1111:2
    #15 0x7f6747067334 in xio_nexus_delayed_close /home/jenkins/openvstorage/accelio/git/src/usr/../common/xio_nexus.c:2211:3
    #16 0x7f67470853ea in kref_sub /home/jenkins/openvstorage/accelio/git/src/usr/linux/kref.h:73:3
    #17 0x7f6747066ff1 in kref_put /home/jenkins/openvstorage/accelio/git/src/usr/linux/kref.h:98:9
    #18 0x7f6747066f3e in xio_nexus_close /home/jenkins/openvstorage/accelio/git/src/usr/../common/xio_nexus.c:2240:2
    #19 0x7f67470cab67 in xio_connection_disconnected /home/jenkins/openvstorage/accelio/git/src/usr/../common/xio_connection.c:2508:4
    #20 0x7f6747005e2b in xio_on_nexus_disconnected /home/jenkins/openvstorage/accelio/git/src/usr/../common/xio_session.c:1126:3
    #21 0x7f6747043487 in xio_client_on_nexus_event /home/jenkins/openvstorage/accelio/git/src/usr/../common/xio_session_client.c:824:3
    #22 0x7f67470503e2 in xio_observable_notify_all_observers /home/jenkins/openvstorage/accelio/git/src/usr/../common/xio_observer.c:223:4
    #23 0x7f6747083602 in xio_nexus_disconnected /home/jenkins/openvstorage/accelio/git/src/usr/../common/xio_nexus.c:1425:3
    #24 0x7f6747076546 in xio_nexus_on_transport_disconnected /home/jenkins/openvstorage/accelio/git/src/usr/../common/xio_nexus.c:1467:2
    #25 0x7f6747058216 in xio_nexus_on_transport_event /home/jenkins/openvstorage/accelio/git/src/usr/../common/xio_nexus.c:1695:3
    #26 0x7f67470503e2 in xio_observable_notify_all_observers /home/jenkins/openvstorage/accelio/git/src/usr/../common/xio_observer.c:223:4
    #27 0x7f6746f3fc3c in xio_transport_notify_observer /home/jenkins/openvstorage/accelio/git/src/common/xio_transport.h:305:2
    #28 0x7f6746f3f5aa in on_sock_disconnected /home/jenkins/openvstorage/accelio/git/src/usr/transport/tcp/xio_tcp_management.c:278:4
    #29 0x7f6746f46291 in xio_tcp_disconnect_handler /home/jenkins/openvstorage/accelio/git/src/usr/transport/tcp/xio_tcp_management.c:521:2