Pierrick Bouvier <pierrick.bouv...@linaro.org> writes:
> On 5/29/24 05:13, Alex Bennée wrote:
>> Pierrick Bouvier <pierrick.bouv...@linaro.org> writes:
>> (Added Philip to CC)
>>
>>> On 5/28/24 12:57, Alex Bennée wrote:
>>>> Pierrick Bouvier <pierrick.bouv...@linaro.org> writes:
>>>>
>>>>> On 5/28/24 12:14, Alex Bennée wrote:
>>>>>> Pierrick Bouvier <pierrick.bouv...@linaro.org> writes:
>>>>>>
>>>>>>> This plugin uses the new time control interface to make decisions
>>>>>>> about the state of time during the emulation. The algorithm is
>>>>>>> currently very simple. The user specifies an ips rate which applies
>>>>>>> per core.
>> <snip>
>>
>>>>>>> +static void vcpu_init(qemu_plugin_id_t id, unsigned int cpu_index)
>>>>>>> +{
>>>>>>> + vCPUTime *vcpu = qemu_plugin_scoreboard_find(vcpus, cpu_index);
>>>>>>> + /* ensure start time is set first */
>>>>>>> + set_start_time();
>>>>>>> + /* start counter from absolute time reference */
>>>>>>> + vcpu->counter = num_insn_during(uptime_ns());
>>>>>>> + vcpu_set_state(vcpu, EXECUTING);
>>>>>>> +}
>>>>>>> +
>>>>>>> +static void vcpu_idle(qemu_plugin_id_t id, unsigned int cpu_index)
>>>>>>> +{
>>>>>>> + vCPUTime *vcpu = qemu_plugin_scoreboard_find(vcpus, cpu_index);
>>>>>>> + vcpu_set_state(vcpu, IDLE);
>>>>>>> +}
>>>>>>> +
>>>>>>> +static void vcpu_resume(qemu_plugin_id_t id, unsigned int cpu_index)
>>>>>>> +{
>>>>>>> + vCPUTime *vcpu = qemu_plugin_scoreboard_find(vcpus, cpu_index);
>>>>>>> + g_assert(vcpu->state == IDLE);
>>>>>> I'm triggering a weird race here:
>>>>>> (gdb) b vcpu_init
>>>>>> Breakpoint 1 at 0x7ffff7fa15f7: file
>>>>>> /home/alex/lsrc/qemu.git/contrib/plugins/ips.c, line 127.
>>>>>> (gdb) r
>>>>>> The program being debugged has been started already.
>>>>>> Start it from the beginning? (y or n) y
>>>>>> Starting program:
>>>>>> /home/alex/lsrc/qemu.git/builds/arm.debug/qemu-system-aarch64
>>>>>> -machine type=virt,virtualization=on,pflash0=rom,pflash1=efivars
>>>>>> -cpu cortex-a57 -smp 32 -accel tcg -device
>>>>>> virtio-net-pci,netdev=unet -device virtio-scsi-pci -device
>>>>>> scsi-hd,drive=hd -netdev user,id=unet,hostfwd=tcp::2222-:22
>>>>>> -blockdev
>>>>>> driver=raw,node-name=hd,file.driver=host_device,file.filename=/dev/zen-ssd2/trixie-arm64,discard=unmap
>>>>>> -serial mon:stdio -blockdev
>>>>>> node-name=rom,driver=file,filename=/home/alex/lsrc/qemu.git/builds/arm.debug/pc-bios/edk2-aarch64-code.fd,read-only=true
>>>>>> -blockdev
>>>>>> node-name=efivars,driver=file,filename=/home/alex/images/qemu-arm64-efivars
>>>>>> -m 8192 -object memory-backend-memfd,id=mem,size=8G,share=on -kernel
>>>>>> /home/alex/lsrc/linux.git/builds/arm64/arch/arm64/boot/Image -append
>>>>>> root=/dev/sda2\ console=ttyAMA0 -plugin
>>>>>> contrib/plugins/libips.so,ips=1000000000
>>>>>> [Thread debugging using libthread_db enabled]
>>>>>> Using host libthread_db library
>>>>>> "/lib/x86_64-linux-gnu/libthread_db.so.1".
>>>>>> [New Thread 0x7fffe72006c0 (LWP 360538)]
>>>>>> [New Thread 0x7fffe68006c0 (LWP 360540)]
>>>>>> [New Thread 0x7fffe5e006c0 (LWP 360541)]
>>>>>> [New Thread 0x7fffe54006c0 (LWP 360542)]
>>>>>> [New Thread 0x7fffe4a006c0 (LWP 360543)]
>>>>>> [New Thread 0x7fffdfe006c0 (LWP 360544)]
>>>>>> [New Thread 0x7fffdf4006c0 (LWP 360545)]
>>>>>> [New Thread 0x7fffdea006c0 (LWP 360546)]
>>>>>> [Switching to Thread 0x7fffdf4006c0 (LWP 360545)]
>>>>>> Thread 8 "qemu-system-aar" hit Breakpoint 1, vcpu_init
>>>>>> (id=10457908569352202058, cpu_index=0) at
>>>>>> /home/alex/lsrc/qemu.git/contrib/plugins/ips.c:127
>>>>>> 127 vCPUTime *vcpu = qemu_plugin_scoreboard_find(vcpus,
>>>>>> cpu_index);
>>>>>> (gdb) c
>>>>>> Continuing.
>>>>>> [New Thread 0x7fffde0006c0 (LWP 360548)]
>>>>>> [Switching to Thread 0x7fffdea006c0 (LWP 360546)]
>>>>>> Thread 9 "qemu-system-aar" hit Breakpoint 1, vcpu_init
>>>>>> (id=10457908569352202058, cpu_index=1) at
>>>>>> /home/alex/lsrc/qemu.git/contrib/plugins/ips.c:127
>>>>>> 127 vCPUTime *vcpu = qemu_plugin_scoreboard_find(vcpus,
>>>>>> cpu_index);
>>>>>> (gdb)
>>>>>> Continuing.
>>>>>> [New Thread 0x7fffdd6006c0 (LWP 360549)]
>>>>>> [Switching to Thread 0x7fffde0006c0 (LWP 360548)]
>>>>>> Thread 10 "qemu-system-aar" hit Breakpoint 1, vcpu_init
>>>>>> (id=10457908569352202058, cpu_index=2) at
>>>>>> /home/alex/lsrc/qemu.git/contrib/plugins/ips.c:127
>>>>>> 127 vCPUTime *vcpu = qemu_plugin_scoreboard_find(vcpus,
>>>>>> cpu_index);
>>>>>> (gdb)
>>>>>> Continuing.
>>>>>> [New Thread 0x7fffdcc006c0 (LWP 360550)]
>>>>>> [Switching to Thread 0x7fffdd6006c0 (LWP 360549)]
>>>>>> Thread 11 "qemu-system-aar" hit Breakpoint 1, vcpu_init
>>>>>> (id=10457908569352202058, cpu_index=3) at
>>>>>> /home/alex/lsrc/qemu.git/contrib/plugins/ips.c:127
>>>>>> 127 vCPUTime *vcpu = qemu_plugin_scoreboard_find(vcpus,
>>>>>> cpu_index);
>>>>>> (gdb)
>>>>>> Continuing.
>>>>>> [New Thread 0x7fffd3e006c0 (LWP 360551)]
>>>>>> [Switching to Thread 0x7fffdcc006c0 (LWP 360550)]
>>>>>> Thread 12 "qemu-system-aar" hit Breakpoint 1, vcpu_init
>>>>>> (id=10457908569352202058, cpu_index=4) at
>>>>>> /home/alex/lsrc/qemu.git/contrib/plugins/ips.c:127
>>>>>> 127 vCPUTime *vcpu = qemu_plugin_scoreboard_find(vcpus,
>>>>>> cpu_index);
>>>>>> (gdb) n
>>>>>> 129 set_start_time();
>>>>>> (gdb)
>>>>>> 131 vcpu->counter = num_insn_during(uptime_ns());
>>>>>> (gdb)
>>>>>> 132 vcpu_set_state(vcpu, EXECUTING);
>>>>>> (gdb)
>>>>>> 133 }
>>>>>> (gdb) p vcpu->state
>>>>>> $1 = EXECUTING
>>>>>> (gdb) p &vcpu->state
>>>>>> $2 = (vCPUState *) 0x555557c6b5d0
>>>>>> (gdb) watch *(vCPUState *) 0x555557c6b5d0
>>>>>> Hardware watchpoint 2: *(vCPUState *) 0x555557c6b5d0
>>>>>> (gdb) c
>>>>>> Continuing.
>>>>>> [Thread 0x7fffdfe006c0 (LWP 360544) exited]
>>>>>> [Thread 0x7fffe5e006c0 (LWP 360541) exited]
>>>>>> Thread 12 "qemu-system-aar" hit Hardware watchpoint 2:
>>>>>> *(vCPUState *) 0x555557c6b5d0
>>>>>> Old value = EXECUTING
>>>>>> New value = IDLE
>>>>>> vcpu_set_state (vcpu=0x555557c6b5c0, new_state=IDLE) at
>>>>>> /home/alex/lsrc/qemu.git/contrib/plugins/ips.c:83
>>>>>> 83 }
>>>>>> (gdb) c
>>>>>> Continuing.
>>>>>> [New Thread 0x7fffdfe006c0 (LWP 360591)]
>>>>>> [New Thread 0x7fffe5e006c0 (LWP 360592)]
>>>>>> [New Thread 0x7fffd34006c0 (LWP 360593)]
>>>>>> [Switching to Thread 0x7fffdfe006c0 (LWP 360591)]
>>>>>> Thread 14 "qemu-system-aar" hit Breakpoint 1, vcpu_init
>>>>>> (id=10457908569352202058, cpu_index=6) at
>>>>>> /home/alex/lsrc/qemu.git/contrib/plugins/ips.c:127
>>>>>> 127 vCPUTime *vcpu = qemu_plugin_scoreboard_find(vcpus,
>>>>>> cpu_index);
>>>>>> (gdb)
>>>>>> Continuing.
>>>>>> [New Thread 0x7fffd2a006c0 (LWP 360594)]
>>>>>> **
>>>>>>
>>>>>> ERROR:/home/alex/lsrc/qemu.git/contrib/plugins/ips.c:144:vcpu_resume:
>>>>>> assertion failed: (vcpu->state == IDLE)
>>>>>> Bail out!
>>>>>> ERROR:/home/alex/lsrc/qemu.git/contrib/plugins/ips.c:144:vcpu_resume:
>>>>>> assertion failed: (vcpu->state == IDLE)
>>>>>> Thread 13 "qemu-system-aar" received signal SIGABRT, Aborted.
>>>>>> [Switching to Thread 0x7fffd3e006c0 (LWP 360551)]
>>>>>> __pthread_kill_implementation (threadid=<optimized out>,
>>>>>> signo=signo@entry=6, no_tid=no_tid@entry=0) at ./nptl/pthread_kill.c:44
>>>>>> 44 ./nptl/pthread_kill.c: No such file or directory.
>>>>>> (gdb) bt
>>>>>> #0 __pthread_kill_implementation (threadid=<optimized out>,
>>>>>> signo=signo@entry=6, no_tid=no_tid@entry=0) at ./nptl/pthread_kill.c:44
>>>>>> #1 0x00007ffff4ca9e8f in __pthread_kill_internal (signo=6,
>>>>>> threadid=<optimized out>) at ./nptl/pthread_kill.c:78
>>>>>> #2 0x00007ffff4c5afb2 in __GI_raise (sig=sig@entry=6) at
>>>>>> ../sysdeps/posix/raise.c:26
>>>>>> #3 0x00007ffff4c45472 in __GI_abort () at ./stdlib/abort.c:79
>>>>>> #4 0x00007ffff6e46ec8 in () at
>>>>>> /lib/x86_64-linux-gnu/libglib-2.0.so.0
>>>>>> #5 0x00007ffff6ea6e1a in g_assertion_message_expr () at
>>>>>> /lib/x86_64-linux-gnu/libglib-2.0.so.0
>>>>>> #6 0x00007ffff7fa16e2 in vcpu_resume (id=10457908569352202058,
>>>>>> cpu_index=5) at /home/alex/lsrc/qemu.git/contrib/plugins/ips.c:144
>>>>>> #7 0x00005555562c3202 in plugin_vcpu_cb__simple
>>>>>> (cpu=0x5555583d9540, ev=QEMU_PLUGIN_EV_VCPU_RESUME) at
>>>>>> ../../plugins/core.c:111
>>>>>> #8 0x00005555562c43f7 in qemu_plugin_vcpu_resume_cb
>>>>>> (cpu=0x5555583d9540) at ../../plugins/core.c:523
>>>>>> #9 0x0000555555d9150e in qemu_wait_io_event (cpu=0x5555583d9540)
>>>>>> at ../../system/cpus.c:465
>>>>>> #10 0x00005555562c67d0 in mttcg_cpu_thread_fn (arg=0x5555583d9540)
>>>>>> at ../../accel/tcg/tcg-accel-ops-mttcg.c:118
>>>>>> #11 0x00005555565120ff in qemu_thread_start (args=0x5555584716e0)
>>>>>> at ../../util/qemu-thread-posix.c:541
>>>>>> #12 0x00007ffff4ca8134 in start_thread (arg=<optimized out>) at
>>>>>> ./nptl/pthread_create.c:442
>>>>>> #13 0x00007ffff4d287dc in clone3 () at
>>>>>> ../sysdeps/unix/sysv/linux/x86_64/clone3.S:81
>>>>>> (gdb)
>>>>>> But I don't understand how we can ever hit the idle callback without
>>>>>> first hitting the init callback.
>>>>>>
>>>>>
>>>>> More exactly, the assert we hit means that the idle callback, was not
>>>>> called before the resume callback.
>>>>> Any chance you can check what is the current vcpu->state value? I
>>>>> wonder if it's not an exited cpu, that gets resumed after.
>>>> No when I looked at it it was set as UNKNOWN. Unfortunately it
>>>> doesn't
>>>> trigger if I stick breakpoints in or run under rr.
>>>>
>>>
>>> By using rr record --chaos mode maybe?
>> Ahh yes that triggered it.
>> It looks like we have a race:
>> (rr) c
>> Continuing.
>> Thread 1 hit Hardware watchpoint 7: *(int *) 0x5559ba6899b0
>> Old value = -1
>> New value = 10
>> machvirt_init (machine=0x5559b9ac3c00) at ../../hw/arm/virt.c:2214
>> 2214 numa_cpu_pre_plug(&possible_cpus->cpus[cs->cpu_index],
>> DEVICE(cpuobj),
>> (rr) c
>> Continuing.
>> [New Thread 650125.650142]
>> [Switching to Thread 650125.650142]
>> Thread 44 hit Breakpoint 8, mttcg_cpu_thread_fn
>> (arg=0x5559ba6896e0) at ../../accel/tcg/tcg-accel-ops-mttcg.c:70
>> 70 assert(tcg_enabled());
>> (rr) p cpu->cpu_index
>> $24 = 10
>> (rr) c
>> Continuing.
>> [Switching to Thread 650125.650125]
>> Thread 1 hit Breakpoint 10, cpu_common_realizefn
>> (dev=0x5559ba6896e0, errp=0x7fff02322c10) at
>> ../../hw/core/cpu-common.c:205
>> 205 Object *machine = qdev_get_machine();
>> (rr) p cpu->cpu_index
>> $25 = 10
>> (rr) bt
>> #0 cpu_common_realizefn (dev=0x5559ba6896e0, errp=0x7fff02322c10) at
>> ../../hw/core/cpu-common.c:205
>> #1 0x00005559b606e6a5 in arm_cpu_realizefn (dev=0x5559ba6896e0,
>> errp=0x7fff02322c10) at ../../target/arm/cpu.c:2552
>> #2 0x00005559b63dd5d0 in device_set_realized (obj=0x5559ba6896e0,
>> value=true, errp=0x7fff02322d20) at ../../hw/core/qdev.c:510
>> #3 0x00005559b63e84e7 in property_set_bool (obj=0x5559ba6896e0,
>> v=0x5559ba681540, name=0x5559b68fafe1 "realized", opaque=0x5559b97f73c0,
>> errp=0x7fff02322d20)
>> at ../../qom/object.c:2354
>> #4 0x00005559b63e6065 in object_property_set (obj=0x5559ba6896e0,
>> name=0x5559b68fafe1 "realized", v=0x5559ba681540, errp=0x7fff02322d20) at
>> ../../qom/object.c:1463
>> #5 0x00005559b63ead1d in object_property_set_qobject
>> (obj=0x5559ba6896e0, name=0x5559b68fafe1 "realized", value=0x5559ba681420,
>> errp=0x5559b7810320 <error_fatal>)
>> at ../../qom/qom-qobject.c:28
>> #6 0x00005559b63e640a in object_property_set_bool (obj=0x5559ba6896e0,
>> name=0x5559b68fafe1 "realized", value=true, errp=0x5559b7810320
>> <error_fatal>)
>> at ../../qom/object.c:1533
>> #7 0x00005559b63dccbd in qdev_realize (dev=0x5559ba6896e0, bus=0x0,
>> errp=0x5559b7810320 <error_fatal>) at ../../hw/core/qdev.c:291
>> #8 0x00005559b5fe4243 in machvirt_init (machine=0x5559b9ac3c00) at
>> ../../hw/arm/virt.c:2295
>> #9 0x00005559b5ada5d6 in machine_run_board_init (machine=0x5559b9ac3c00,
>> mem_path=0x0, errp=0x7fff02322f30) at ../../hw/core/machine.c:1576
>> #10 0x00005559b5eb416f in qemu_init_board () at ../../system/vl.c:2621
>> #11 0x00005559b5eb4482 in qmp_x_exit_preconfig (errp=0x5559b7810320
>> <error_fatal>) at ../../system/vl.c:2713
>> #12 0x00005559b5eb7088 in qemu_init (argc=35, argv=0x7fff02323268) at
>> ../../system/vl.c:3759
>> #13 0x00005559b63d7ff2 in main (argc=35, argv=0x7fff02323268) at
>> ../../system/main.c:47
>> Because looking at the order things happen in the specific CPU
>> realisation:
>> qemu_init_vcpu(cs);
>> cpu_reset(cs);
>> acc->parent_realize(dev, errp);
>> And the common realize function doesn't get to do:
>> /* Plugin initialization must wait until the cpu start
>> executing code */
>> #ifdef CONFIG_PLUGIN
>> if (tcg_enabled()) {
>> cpu->plugin_state = qemu_plugin_create_vcpu_state();
>> async_run_on_cpu(cpu, qemu_plugin_vcpu_init__async,
>> RUN_ON_CPU_NULL);
>> }
>> #endif
>> before we've started executing.....
>>
>
> Thanks for the analysis Alex.
> It seems to me this is integrating the recent series from Philippe.
> Maybe the race has been introduced there.
> Could you try without this series?
No this is based off master and I think the race has always been there.
I think I was just triggering because I was using -smp 32 for some bit
system simulations. See:
Message-Id: <20240529152219.825680-1-alex.ben...@linaro.org>
Date: Wed, 29 May 2024 16:22:19 +0100
Subject: [RFC PATCH] cpus: split qemu_init_vcpu and delay vCPU thread creation
From: =?UTF-8?q?Alex=20Benn=C3=A9e?= <alex.ben...@linaro.org>
--
Alex Bennée
Virtualisation Tech Lead @ Linaro
