Re: [Qemu-devel] [PATCH v4 2/2] char-socket: Lock tcp_chr_disconnect() and socket_reconnect_timeout()

[Daniel P . Berrangé]

On Mon, Aug 12, 2019 at 06:58:29PM +0300, Andrey Shinkevich wrote:
> From: Alberto Garcia <address@hidden>
> 
> There's a race condition in which the tcp_chr_read() ioc handler can
> close a connection that is being written to from another thread.
> 
> Running iotest 136 in a loop triggers this problem and crashes QEMU.
> 
>  (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 patch adds a lock to protect tcp_chr_disconnect() and
> socket_reconnect_timeout()
> 
> Signed-off-by: Alberto Garcia <address@hidden>
> Signed-off-by: Andrey Shinkevich <address@hidden>

Reviewed-by: Daniel P. Berrangé <address@hidden>


Regards,
Daniel
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