Re: [Qemu-devel] another locking issue in current dataplane code?

[Ming Lei]

On Tue, Jul 8, 2014 at 3:19 PM, Christian Borntraeger
<address@hidden> wrote:
> Ping.
>
> has anyone seen a similar hang on x86?
>
>
>
> On 07/07/14 13:58, Christian Borntraeger wrote:
>> Folks,
>>
>> with current 2.1-rc0 (
>> +  dataplane: do not free VirtQueueElement in vring_push()
>> +  virtio-blk: avoid dataplane VirtIOBlockReq early free
>> + some not-ready yet s390 patches for migration
>> )
>>
>> I still having issues with dataplane during managedsave (without dataplane 
>> everything seems to work fine):
>>
>> With 1 CPU and 1 disk (and some workload, e.g. a simple dd on the disk) I 
>> get:
>>
>>
>> Thread 3 (Thread 0x3fff90fd910 (LWP 27218)):
>> #0  0x000003fffcdb7ba0 in __lll_lock_wait () from /lib64/libpthread.so.0
>> #1  0x000003fffcdbac0c in __pthread_mutex_cond_lock () from 
>> /lib64/libpthread.so.0
>> #2  0x000003fffcdb399a in pthread_cond_wait@@GLIBC_2.3.2 () from 
>> /lib64/libpthread.so.0
>> #3  0x00000000801fff06 in qemu_cond_wait (cond=<optimized out>, 
>> address@hidden <qemu_global_mutex>) at 
>> /home/cborntra/REPOS/qemu/util/qemu-thread-posix.c:135
>> #4  0x00000000800472f4 in qemu_kvm_wait_io_event (cpu=<optimized out>) at 
>> /home/cborntra/REPOS/qemu/cpus.c:843
>> #5  qemu_kvm_cpu_thread_fn (arg=0x809ad6b0) at 
>> /home/cborntra/REPOS/qemu/cpus.c:879
>> #6  0x000003fffcdaf412 in start_thread () from /lib64/libpthread.so.0
>> #7  0x000003fffba350ae in thread_start () from /lib64/libc.so.6
>>
>> Thread 2 (Thread 0x3fff88fd910 (LWP 27219)):
>> #0  0x000003fffba2a8e0 in ppoll () from /lib64/libc.so.6
>> #1  0x00000000801af250 in ppoll (__ss=0x0, __timeout=0x0, __nfds=<optimized 
>> out>, __fds=<optimized out>) at /usr/include/bits/poll2.h:77
>> #2  qemu_poll_ns (address@hidden, address@hidden, timeout=-1) at 
>> /home/cborntra/REPOS/qemu/qemu-timer.c:314
>> #3  0x00000000801b0702 in aio_poll (ctx=0x807f2230, address@hidden) at 
>> /home/cborntra/REPOS/qemu/aio-posix.c:221
>> #4  0x00000000800be3c4 in iothread_run (opaque=0x807f20d8) at 
>> /home/cborntra/REPOS/qemu/iothread.c:41
>> #5  0x000003fffcdaf412 in start_thread () from /lib64/libpthread.so.0
>> #6  0x000003fffba350ae in thread_start () from /lib64/libc.so.6
>>
>> Thread 1 (Thread 0x3fff9c529b0 (LWP 27215)):
>> #0  0x000003fffcdb38f0 in pthread_cond_wait@@GLIBC_2.3.2 () from 
>> /lib64/libpthread.so.0
>> #1  0x00000000801fff06 in qemu_cond_wait (address@hidden, address@hidden) at 
>> /home/cborntra/REPOS/qemu/util/qemu-thread-posix.c:135
>> #2  0x0000000080212906 in rfifolock_lock (address@hidden) at 
>> /home/cborntra/REPOS/qemu/util/rfifolock.c:59
>> #3  0x000000008019e536 in aio_context_acquire (address@hidden) at 
>> /home/cborntra/REPOS/qemu/async.c:295
>> #4  0x00000000801a34e6 in bdrv_drain_all () at 
>> /home/cborntra/REPOS/qemu/block.c:1907
>> #5  0x0000000080048e24 in do_vm_stop (state=RUN_STATE_PAUSED) at 
>> /home/cborntra/REPOS/qemu/cpus.c:538
>> #6  vm_stop (address@hidden) at /home/cborntra/REPOS/qemu/cpus.c:1221
>> #7  0x00000000800e6338 in qmp_stop (address@hidden) at 
>> /home/cborntra/REPOS/qemu/qmp.c:98
>> #8  0x00000000800e1314 in qmp_marshal_input_stop (mon=<optimized out>, 
>> qdict=<optimized out>, ret=<optimized out>) at qmp-marshal.c:2806
>> #9  0x000000008004b91a in qmp_call_cmd (cmd=<optimized out>, 
>> params=0x8096cf50, mon=0x8080b8a0) at 
>> /home/cborntra/REPOS/qemu/monitor.c:5038
>> #10 handle_qmp_command (parser=<optimized out>, tokens=<optimized out>) at 
>> /home/cborntra/REPOS/qemu/monitor.c:5104
>> #11 0x00000000801faf16 in json_message_process_token (lexer=0x8080b7c0, 
>> token=0x808f2610, type=<optimized out>, x=<optimized out>, y=6) at 
>> /home/cborntra/REPOS/qemu/qobject/json-streamer.c:87
>> #12 0x0000000080212bac in json_lexer_feed_char (address@hidden, 
>> ch=<optimized out>, address@hidden) at 
>> /home/cborntra/REPOS/qemu/qobject/json-lexer.c:303
>> #13 0x0000000080212cfe in json_lexer_feed (lexer=0x8080b7c0, 
>> buffer=<optimized out>, size=<optimized out>) at 
>> /home/cborntra/REPOS/qemu/qobject/json-lexer.c:356
>> #14 0x00000000801fb10e in json_message_parser_feed (parser=<optimized out>, 
>> buffer=<optimized out>, size=<optimized out>) at 
>> /home/cborntra/REPOS/qemu/qobject/json-streamer.c:110
>> #15 0x0000000080049f28 in monitor_control_read (opaque=<optimized out>, 
>> buf=<optimized out>, size=<optimized out>) at 
>> /home/cborntra/REPOS/qemu/monitor.c:5125
>> #16 0x00000000800c8636 in qemu_chr_be_write (len=1, buf=0x3ffffa9e010 
>> "}[B\377\373\251\372\b", s=0x807f5af0) at 
>> /home/cborntra/REPOS/qemu/qemu-char.c:213
>> #17 tcp_chr_read (chan=<optimized out>, cond=<optimized out>, 
>> opaque=0x807f5af0) at /home/cborntra/REPOS/qemu/qemu-char.c:2690
>> #18 0x000003fffcc9f05a in g_main_context_dispatch () from 
>> /lib64/libglib-2.0.so.0
>> #19 0x00000000801ae3e0 in glib_pollfds_poll () at 
>> /home/cborntra/REPOS/qemu/main-loop.c:190
>> #20 os_host_main_loop_wait (timeout=<optimized out>) at 
>> /home/cborntra/REPOS/qemu/main-loop.c:235
>> #21 main_loop_wait (nonblocking=<optimized out>) at 
>> /home/cborntra/REPOS/qemu/main-loop.c:484
>> #22 0x00000000800169e2 in main_loop () at /home/cborntra/REPOS/qemu/vl.c:2024
>> #23 main (argc=<optimized out>, argv=<optimized out>, envp=<optimized out>) 
>> at /home/cborntra/REPOS/qemu/vl.c:4551
>>
>> Now. If aio_poll never returns, we have a deadlock here.
>> To me it looks like, that aio_poll could be called from iothread_run, even 
>> if there are no outstanding request.
>> Opinions?

I have sent out one patch to fix the issue, and the title is
"virtio-blk: data-plane: fix save/set .complete_request in start".

Please try this patch to see if it fixes your issue.

thanks