Re: [PULL 09/14] qmp: Move dispatcher to a coroutine

[Kevin Wolf]

Am 12.10.2020 um 13:53 hat Philippe Mathieu-Daudé geschrieben:
> On 10/12/20 1:25 PM, Kevin Wolf wrote:
> > Am 12.10.2020 um 12:47 hat Alex Bennée geschrieben:
> > > 
> > > Markus Armbruster <armbru@redhat.com> writes:
> > > 
> > > > From: Kevin Wolf <kwolf@redhat.com>
> > > > 
> > > > This moves the QMP dispatcher to a coroutine and runs all QMP command
> > > > handlers that declare 'coroutine': true in coroutine context so they
> > > > can avoid blocking the main loop while doing I/O or waiting for other
> > > > events.
> > > 
> > > This subtly changes the replay behaviour leading to a hang in:
> > > 
> > >    10:55:18 [alex.bennee@hackbox2:~/l/q/b/bisect] (625581c2…)|✚1(+1/-1) + 
> > > ./tests/venv/bin/avocado run 
> > > tests/acceptance/replay_kernel.py:ReplayKernel.test_arm_virt
> > >    Fetching asset from 
> > > tests/acceptance/replay_kernel.py:ReplayKernel.test_arm_virt
> > >    JOB ID     : ec11fd2544f06e6c0d421f16afa757b49f7ed734
> > >    JOB LOG    : 
> > > /home/alex.bennee/avocado/job-results/job-2020-10-12T11.40-ec11fd2/job.log
> > >     (1/1) tests/acceptance/replay_kernel.py:ReplayKernel.test_arm_virt: 
> > > ERROR: Could not perform graceful shutdown (26.27 s)
> > >    RESULTS    : PASS 0 | ERROR 1 | FAIL 0 | SKIP 0 | WARN 0 | INTERRUPT 0 
> > > | CANCEL 0
> > >    JOB TIME   : 27.77 s
> > > 
> > > Looking at the log:
> > > 
> > >    2020-10-12 11:40:31,426 __init__         L0085 DEBUG| [    3.887411] 
> > > rtc-pl031 9010000.pl031: setting system clock to 2020-10-12 10:40:31 UTC 
> > > (1602499231)
> > >    2020-10-12 11:40:31,428 __init__         L0085 DEBUG| [    3.887431] 
> > > sr_init: No PMIC hook to init smartreflex
> > >    2020-10-12 11:40:31,447 __init__         L0085 DEBUG| [    3.897193] 
> > > uart-pl011 9000000.pl011: no DMA platform data
> > >    2020-10-12 11:40:31,460 __init__         L0085 DEBUG| [    3.897242] 
> > > md: Waiting for all devices to be available before autodetect
> > >    2020-10-12 11:40:31,462 __init__         L0085 DEBUG| [    3.897259] 
> > > md: If you don't use raid, use raid=noautodetect
> > >    2020-10-12 11:40:31,475 __init__         L0085 DEBUG| [    3.897819] 
> > > md: Autodetecting RAID arrays.
> > >    2020-10-12 11:40:31,476 __init__         L0085 DEBUG| [    3.897832] 
> > > md: autorun ...
> > >    2020-10-12 11:40:31,477 __init__         L0085 DEBUG| [    3.897842] 
> > > md: ... autorun DONE.
> > >    2020-10-12 11:40:31,483 __init__         L0085 DEBUG| [    3.897962] 
> > > VFS: Cannot open root device "(null)" or unknown-block(0,0): error -6
> > >    2020-10-12 11:40:31,483 qmp              L0245 DEBUG| >>> {'execute': 
> > > 'quit'}
> > >    2020-10-12 11:40:31,495 qmp              L0145 DEBUG| <<< 
> > > {'timestamp': {'seconds': 1602499231, 'microseconds': 493379}, 'event': 
> > > 'SHUTDOWN', 'data': {'guest': True, 'reason': 'guest-reset'}}
> > >    2020-10-12 11:40:31,733 machine          L0325 WARNI| qemu received 
> > > signal 6; command: "./qemu-system-arm -display none -vga none -chardev 
> > > socket,id=mon,path=/var/tmp/tmpzls53khe/qemu-8487-monitor.sock -mon 
> > > chardev=mon,mode=control -machine virt -chardev 
> > > socket,id=console,path=/var/tmp/tmpzls53khe/qemu-8487-console.sock,server,nowait
> > >  -serial chardev:console -icount 
> > > shift=1,rr=record,rrfile=/var/tmp/avocado_n00stdrf/avocado_job_aw60qdul/1-tests_acceptance_replay_kernel.py_ReplayKernel.test_arm_virt/replay.bin
> > >  -kernel 
> > > /home/alex.bennee/avocado/data/cache/by_location/62750ce9e069e69e6a7ff04ff54c382ee660b92a/vmlinuz
> > >  -append printk.time=1 panic=-1 console=ttyAMA0 -net none -no-reboot"
> > 
> > This looks like a crash (SIGABRT) rather than a hang. Do you have a
> > stack trace for the crashed process?
> 
> No crash, exit(0):

Why does the log say "qemu received signal 6" then?

> VFS: Cannot open root device "(null)" or unknown-block(0,0): error -6

Alex has this error in the logs before this commit, so I assume this is
expected. All of the following is then probably expected, too, because
it follows directly from this error:

> Please append a correct "root=" boot option; here are the available
> partitions:
> Kernel panic - not syncing: VFS: Unable to mount root fs on
> unknown-block(0,0)
> CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.18.16-300.fc29.armv7hl #1
> Hardware name: Generic DT based system
> [<c0313f7c>] (unwind_backtrace) from [<c030dc64>] (show_stack+0x20/0x24)
> [<c030dc64>] (show_stack) from [<c0b50ec4>] (dump_stack+0x88/0xa8)
> [<c0b50ec4>] (dump_stack) from [<c03592f8>] (panic+0xd4/0x26c)
> [<c03592f8>] (panic) from [<c110183c>] (mount_block_root+0x250/0x2ec)
> [<c110183c>] (mount_block_root) from [<c1101950>] (mount_root+0x78/0x90)
> [<c1101950>] (mount_root) from [<c1101ac4>] (prepare_namespace+0x15c/0x19c)
> [<c1101ac4>] (prepare_namespace) from [<c11012e8>]
> (kernel_init_freeable+0x2c0/0x370)
> [<c11012e8>] (kernel_init_freeable) from [<c0b63914>]
> (kernel_init+0x18/0x128)
> [<c0b63914>] (kernel_init) from [<c03010e8>] (ret_from_fork+0x14/0x2c)
> Exception stack(0xc790bfb0 to 0xc790bff8)
> bfa0:                                     00000000 00000000 00000000
> 00000000
> bfc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000
> 00000000
> bfe0: 00000000 00000000 00000000 00000000 00000013 00000000
> 
> -> PSCI call
>    -> QEMU_PSCI_0_2_FN_SYSTEM_RESET
>       -> SHUTDOWN_CAUSE_GUEST_RESET
>          -> exit(0)

Hm... So you're saying that the test sends a 'quit' QMP command, but
before it could be processed, the guest causes QEMU to exit, so the test
will never receive a reply to its request?

If commit 9ce44e2ce2 changes anything about this, it seems to me that it
would be that more QMP commands are processed during monitor_cleanup()
because it doesn't just delete the dispatcher BH, but waits until it's
not busy any more.

Looking at this code again, however, the order in monitor_cleanup() is
probably wrong. We should first shut down the dispatcher (which may
still be using Monitor objects) and then destroy the monitors. This
could possibly explain a crash, but probably not wrong results with a
successful shutdown.

Kevin

> > >    2020-10-12 11:40:31,734 stacktrace       L0039 ERROR|
> > >    2020-10-12 11:40:31,734 stacktrace       L0042 ERROR| Reproduced 
> > > traceback from: 
> > > /home/alex.bennee/lsrc/qemu.git/builds/bisect/tests/venv/lib/python3.6/site-packages/avocado/core/test.py:767
> > >    2020-10-12 11:40:31,735 stacktrace       L0045 ERROR| Traceback (most 
> > > recent call last):
> > >    2020-10-12 11:40:31,735 stacktrace       L0045 ERROR|   File 
> > > "/home/alex.bennee/lsrc/qemu.git/python/qemu/machine.py", line 435, in 
> > > _do_shutdown
> > >    2020-10-12 11:40:31,735 stacktrace       L0045 ERROR|     
> > > self._soft_shutdown(timeout, has_quit)
> > >    2020-10-12 11:40:31,735 stacktrace       L0045 ERROR|   File 
> > > "/home/alex.bennee/lsrc/qemu.git/python/qemu/machine.py", line 415, in 
> > > _soft_shutdown
> > >    2020-10-12 11:40:31,735 stacktrace       L0045 ERROR|     
> > > self._qmp.cmd('quit')
> > >    2020-10-12 11:40:31,735 stacktrace       L0045 ERROR|   File 
> > > "/home/alex.bennee/lsrc/qemu.git/python/qemu/qmp.py", line 266, in cmd
> > >    2020-10-12 11:40:31,735 stacktrace       L0045 ERROR|     return 
> > > self.cmd_obj(qmp_cmd)
> > >    2020-10-12 11:40:31,735 stacktrace       L0045 ERROR|   File 
> > > "/home/alex.bennee/lsrc/qemu.git/python/qemu/qmp.py", line 249, in cmd_obj
> > >    2020-10-12 11:40:31,736 stacktrace       L0045 ERROR|     raise 
> > > QMPConnectError("Unexpected empty reply from server")
> > >    2020-10-12 11:40:31,736 stacktrace       L0045 ERROR| 
> > > qemu.qmp.QMPConnectError: Unexpected empty reply from server
> > >    2020-10-12 11:40:31,736 stacktrace       L0045 ERROR|
> > >    2020-10-12 11:40:31,736 stacktrace       L0045 ERROR| The above 
> > > exception was the direct cause of the following exception:
> > >    2020-10-12 11:40:31,736 stacktrace       L0045 ERROR|
> > >    2020-10-12 11:40:31,736 stacktrace       L0045 ERROR| Traceback (most 
> > > recent call last):
> > >    2020-10-12 11:40:31,736 stacktrace       L0045 ERROR|   File 
> > > "/home/alex.bennee/lsrc/qemu.git/builds/bisect/tests/acceptance/replay_kernel.py",
> > >  line 128, in test_arm_virt
> > >    2020-10-12 11:40:31,736 stacktrace       L0045 ERROR|     
> > > self.run_rr(kernel_path, kernel_command_line, console_pattern, shift=1)
> > >    2020-10-12 11:40:31,736 stacktrace       L0045 ERROR|   File 
> > > "/home/alex.bennee/lsrc/qemu.git/builds/bisect/tests/acceptance/replay_kernel.py",
> > >  line 71, in run_rr
> > >    2020-10-12 11:40:31,736 stacktrace       L0045 ERROR|     True, shift, 
> > > args, replay_path)
> > >    2020-10-12 11:40:31,736 stacktrace       L0045 ERROR|   File 
> > > "/home/alex.bennee/lsrc/qemu.git/builds/bisect/tests/acceptance/replay_kernel.py",
> > >  line 57, in run_vm
> > >    2020-10-12 11:40:31,736 stacktrace       L0045 ERROR|     vm.shutdown()
> > >    2020-10-12 11:40:31,736 stacktrace       L0045 ERROR|   File 
> > > "/home/alex.bennee/lsrc/qemu.git/python/qemu/machine.py", line 465, in 
> > > shutdown
> > >    2020-10-12 11:40:31,736 stacktrace       L0045 ERROR|     
> > > self._do_shutdown(timeout, has_quit)
> > >    2020-10-12 11:40:31,736 stacktrace       L0045 ERROR|   File 
> > > "/home/alex.bennee/lsrc/qemu.git/python/qemu/machine.py", line 439, in 
> > > _do_shutdown
> > >    2020-10-12 11:40:31,736 stacktrace       L0045 ERROR|     from exc
> > >    2020-10-12 11:40:31,737 stacktrace       L0045 ERROR| 
> > > qemu.machine.AbnormalShutdown: Could not perform graceful shutdown
> > > 
> > > The commit before:
> > > 
> > >    2020-10-12 11:44:02,803 __init__         L0085 DEBUG| [    3.897837] 
> > > md: ... autorun DONE.
> > >    2020-10-12 11:44:02,806 __init__         L0085 DEBUG| [    3.897958] 
> > > VFS: Cannot open root device "(null)" or unknown-block(0,0): error -6
> > >    2020-10-12 11:44:02,806 qmp              L0245 DEBUG| >>> {'execute': 
> > > 'quit'}
> > >    2020-10-12 11:44:02,814 qmp              L0250 DEBUG| <<< {'return': 
> > > {}}
> > >    2020-10-12 11:44:02,879 replay_kernel    L0059 INFO | finished the 
> > > recording with log size 237596 bytes
> > >    2020-10-12 11:44:02,879 replay_kernel    L0064 INFO | elapsed time 
> > > 24.35 sec
> > >    2020-10-12 11:44:02,888 replay_kernel    L0044 INFO | replaying the 
> > > execution...
> > >    2020-10-12 11:44:02,889 machine          L0362 DEBUG| VM launch 
> > > command: './qemu-system-arm -display none -vga none -chardev 
> > > socket,id=mon,path=/var/tmp/tmpihqswp6_/qemu-7747-monitor.sock -mon 
> > > chardev=mon,mode=control -machine virt -chardev 
> > > socket,id=console,path=/var/tmp/tmpihqswp6_/qemu-7747-console.sock,server,nowait
> > >  -serial chardev:console
> > >    -icount 
> > > shift=1,rr=replay,rrfile=/var/tmp/avocado_o3pfy2he/avocado_job_nf30vjqg/1-tests_acceptance_replay_kernel.py_ReplayKernel.test_arm_virt/replay.bin
> > >  -kernel 
> > > /home/alex.bennee/avocado/data/cache/by_location/62750ce9e069e69e6a7ff04ff54c382ee660b92a/vmlinuz
> > >  -append printk.time=1 panic=-1 console=ttyAMA0 -net none -no-reboot'
> > >    2020-10-12 11:44:03,001 qmp              L0245 DEBUG| >>> {'execute': 
> > > 'qmp_capabilities'}
> > >    2020-10-12 11:44:03,172 qmp              L0250 DEBUG| <<< {'return': 
> > > {}}
> > >    2020-10-12 11:44:04,899 __init__         L0085 DEBUG| [    0.000000] 
> > > Booting Linux on physical CPU 0x0
> > >    2020-10-12 11:44:04,904 __init__         L0085 DEBUG| [    0.000000] 
> > > Linux version 4.18.16-300.fc29.armv7hl 
> > > (mockbuild@buildvm-armv7-06.arm.fedoraproject.org) (gcc version 8.2.1 
> > > 20180801 (Red Hat 8.2.1-2) (GCC)) #1 SMP Sun Oct 21 00:56:28 UTC 2018
> [...]
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