On Wed 06 Feb 2019 01:49:02 PM CET, Daniel P. Berrangé wrote:
>> (gdb) bt
>> #0 0x00005558b842902d in object_get_class (obj=0x0) at qom/object.c:860
>> #1 0x00005558b84f92db in qio_channel_writev_full (ioc=0x0,
>> iov=0x7ffc355decf0, niov=1, fds=0x0, nfds=0, errp=0x0) at io/channel.c:76
>> #2 0x00005558b84e0e9e in io_channel_send_full (ioc=0x0,
>> buf=0x5558baf5beb0, len=138, fds=0x0, nfds=0) at chardev/char-io.c:123
>> #3 0x00005558b84e4a69 in tcp_chr_write (chr=0x5558ba460380,
>> buf=0x5558baf5beb0 "...", len=138) at chardev/char-socket.c:135
>> #4 0x00005558b84dca55 in qemu_chr_write_buffer (s=0x5558ba460380,
>> buf=0x5558baf5beb0 "...", len=138, offset=0x7ffc355dedd0, write_all=false)
>> at chardev/char.c:112
>> #5 0x00005558b84dcbc2 in qemu_chr_write (s=0x5558ba460380,
>> buf=0x5558baf5beb0 "...", len=138, write_all=false) at chardev/char.c:147
>> #6 0x00005558b84dfb26 in qemu_chr_fe_write (be=0x5558ba476610,
>> buf=0x5558baf5beb0 "...", len=138) at chardev/char-fe.c:42
>> #7 0x00005558b8088c86 in monitor_flush_locked (mon=0x5558ba476610) at
>> monitor.c:406
>> #8 0x00005558b8088e8c in monitor_puts (mon=0x5558ba476610,
>> str=0x5558ba921e49 "") at monitor.c:449
>> #9 0x00005558b8089178 in qmp_send_response (mon=0x5558ba476610,
>> rsp=0x5558bb161600) at monitor.c:498
>> #10 0x00005558b808920c in monitor_qapi_event_emit
>> (event=QAPI_EVENT_SHUTDOWN, qdict=0x5558bb161600) at monitor.c:526
>> #11 0x00005558b8089307 in monitor_qapi_event_queue_no_reenter
>> (event=QAPI_EVENT_SHUTDOWN, qdict=0x5558bb161600) at monitor.c:551
>> #12 0x00005558b80896c0 in qapi_event_emit (event=QAPI_EVENT_SHUTDOWN,
>> qdict=0x5558bb161600) at monitor.c:626
>> #13 0x00005558b855f23b in qapi_event_send_shutdown (guest=false,
>> reason=SHUTDOWN_CAUSE_HOST_QMP_QUIT) at qapi/qapi-events-run-state.c:43
>> #14 0x00005558b81911ef in qemu_system_shutdown
>> (cause=SHUTDOWN_CAUSE_HOST_QMP_QUIT) at vl.c:1837
>> #15 0x00005558b8191308 in main_loop_should_exit () at vl.c:1885
>> #16 0x00005558b819140d in main_loop () at vl.c:1924
>> #17 0x00005558b8198c84 in main (argc=18, argv=0x7ffc355df3f8,
>> envp=0x7ffc355df490) at vl.c:4665
>
> This shows the main thread trace - i'd be interested to see a trace of
> the other thread which is calling tcp_chr_free_connection() to
> understand why we have 2 threads racing at all.
The other thread is already done by the time this one crashes, but you
can see what's going on if you replace the qemu_mutex_lock() call in
this patch with a trylock() + an assertion:
#0 __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:51
#1 0x00007fafc05e642a in __GI_abort () at abort.c:89
#2 0x00007fafc05dde67 in __assert_fail_base (fmt=<optimized out>,
assertion=assertion@entry=0x55a4dbe78448
"qemu_mutex_trylock(&chr->chr_write_lock) != -EBUSY",
file=file@entry=0x55a4dbe78320 "chardev/char-socket.c",
line=line@entry=452,
function=function@entry=0x55a4dbe788d0 <__PRETTY_FUNCTION__.20007>
"tcp_chr_disconnect") at assert.c:92
#3 0x00007fafc05ddf12 in __GI___assert_fail (assertion=0x55a4dbe78448
"qemu_mutex_trylock(&chr->chr_write_lock) != -EBUSY",
file=0x55a4dbe78320 "chardev/char-socket.c", line=452,
function=0x55a4dbe788d0 <__PRETTY_FUNCTION__.20007> "tcp_chr_disconnect")
at assert.c:101
#4 0x000055a4dbbbdab1 in tcp_chr_disconnect (chr=0x55a4dc76e380) at
chardev/char-socket.c:452
#5 0x000055a4dbbbdca0 in tcp_chr_read (chan=0x55a4dc76e770, cond=(G_IO_IN |
G_IO_HUP), opaque=0x55a4dc76e380) at chardev/char-socket.c:486
#6 0x000055a4dbbd7f76 in qio_channel_fd_source_dispatch
(source=0x7fafac005000, callback=0x55a4dbbbdb5c <tcp_chr_read>,
user_data=0x55a4dc76e380)
at io/channel-watch.c:84
#7 0x00007fafc3ad16aa in g_main_context_dispatch () from
/lib/x86_64-linux-gnu/libglib-2.0.so.0
#8 0x00007fafc3ad1a60 in ?? () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
#9 0x00007fafc3ad1d82 in g_main_loop_run () from
/lib/x86_64-linux-gnu/libglib-2.0.so.0
#10 0x000055a4db8601f9 in iothread_run (opaque=0x55a4dc781440) at iothread.c:74
#11 0x000055a4dbc57039 in qemu_thread_start (args=0x55a4dc774c10) at
util/qemu-thread-posix.c:502
#12 0x00007fafc0958494 in start_thread (arg=0x7fafb23aa700) at
pthread_create.c:333
#13 0x00007fafc069aacf in clone () at
../sysdeps/unix/sysv/linux/x86_64/clone.S:97
Berto
