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

[Christian Borntraeger]

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?
> 
> Christian
> 
>