Re: [PATCH RFC 10/10] tests/migration-tests: Add test case for responsive CPU throttle

[Fabiano Rosas <farosas@suse.de>]

Fabiano Rosas <farosas@suse.de> writes:

> Peter Xu <peterx@redhat.com> writes:
>
>> On Thu, Sep 12, 2024 at 09:13:16AM +0100, Peter Maydell wrote:
>>> On Wed, 11 Sept 2024 at 22:26, Fabiano Rosas <farosas@suse.de> wrote:
>>> > I don't think we're discussing total CI time at this point, so the math
>>> > doesn't really add up. We're not looking into making the CI finish
>>> > faster. We're looking into making migration-test finish faster. That
>>> > would reduce timeouts in CI, speed-up make check and reduce the chance
>>> > of random race conditions* affecting other people/staging runs.
>>> 
>>> Right. The reason migration-test appears on my radar is because
>>> it is very frequently the thing that shows up as "this sometimes
>>> just fails or just times out and if you hit retry it goes away
>>> again". That might not be migration-test's fault specifically,
>>> because those retries tend to be certain CI configs (s390,
>>> the i686-tci one), and I have some theories about what might be
>>> causing it (e.g. build system runs 4 migration-tests in parallel,
>>> which means 8 QEMU processes which is too many for the number
>>> of host CPUs). But right now I look at CI job failures and my reaction
>>> is "oh, it's the migration-test failing yet again" :-(
>>> 
>>> For some examples from this week:
>>> 
>>> https://gitlab.com/qemu-project/qemu/-/jobs/7802183144
>>> https://gitlab.com/qemu-project/qemu/-/jobs/7799842373  <--------[1]
>>> https://gitlab.com/qemu-project/qemu/-/jobs/7786579152  <--------[2]
>>> https://gitlab.com/qemu-project/qemu/-/jobs/7786579155
>>
>> Ah right, the TIMEOUT is unfortunate, especially if tests can be run in
>> parallel.  It indeed sounds like no good way to finally solve.. I don't
>> also see how speeding up / reducing tests in migration test would help, as
>> that's (from some degree..) is the same as tuning the timeout value bigger.
>> When the tests are less it'll fit into 480s window, but maybe it's too
>> quick now we wonder whether we should shrink it to e.g. 90s, but then it
>> can timeout again when on a busy host with less capability of concurrency.
>>
>> But indeed there're two ERRORs ([1,2] above)..  I collected some more info
>> here before the log expires:
>>
>> =================================8<================================
>>
>> *** /i386/migration/multifd/tcp/plain/cancel, qtest-i386 on s390 host
>>
>> https://gitlab.com/qemu-project/qemu/-/jobs/7799842373
>>
>> 101/953 qemu:qtest+qtest-i386 / qtest-i386/migration-test                         ERROR          144.32s   killed by signal 6 SIGABRT
>>>>> QTEST_QEMU_STORAGE_DAEMON_BINARY=./storage-daemon/qemu-storage-daemon G_TEST_DBUS_DAEMON=/home/gitlab-runner/builds/zEr9wY_L/0/qemu-project/qemu/tests/dbus-vmstate-daemon.sh PYTHON=/home/gitlab-runner/builds/zEr9wY_L/0/qemu-project/qemu/build/pyvenv/bin/python3 QTEST_QEMU_IMG=./qemu-img MALLOC_PERTURB_=144 QTEST_QEMU_BINARY=./qemu-system-i386 /home/gitlab-runner/builds/zEr9wY_L/0/qemu-project/qemu/build/tests/qtest/migration-test --tap -k
>> ――――――――――――――――――――――――――――――――――――― ✀  ―――――――――――――――――――――――――――――――――――――
>> stderr:
>> warning: fd: migration to a file is deprecated. Use file: instead.
>> warning: fd: migration to a file is deprecated. Use file: instead.
>> ../tests/qtest/libqtest.c:205: kill_qemu() detected QEMU death from signal 11 (Segmentation fault) (core dumped)
>> (test program exited with status code -6)
>> TAP parsing error: Too few tests run (expected 53, got 39)
>> ――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――
>>
>> # Start of plain tests
>> # Running /i386/migration/multifd/tcp/plain/cancel
>> # Using machine type: pc-i440fx-9.2
>> # starting QEMU: exec ./qemu-system-i386 -qtest unix:/tmp/qtest-3273509.sock -qtest-log /dev/null -chardev socket,path=/tmp/qtest-3273509.qmp,id=char0 -mon chardev=char0,mode=control -display none -audio none -accel kvm -accel tcg -machine pc-i440fx-9.2, -name source,debug-threads=on -m 150M -serial file:/tmp/migration-test-4112T2/src_serial -drive if=none,id=d0,file=/tmp/migration-test-4112T2/bootsect,format=raw -device ide-hd,drive=d0,secs=1,cyls=1,heads=1    2>/dev/null -accel qtest
>> # starting QEMU: exec ./qemu-system-i386 -qtest unix:/tmp/qtest-3273509.sock -qtest-log /dev/null -chardev socket,path=/tmp/qtest-3273509.qmp,id=char0 -mon chardev=char0,mode=control -display none -audio none -accel kvm -accel tcg -machine pc-i440fx-9.2, -name target,debug-threads=on -m 150M -serial file:/tmp/migration-test-4112T2/dest_serial -incoming defer -drive if=none,id=d0,file=/tmp/migration-test-4112T2/bootsect,format=raw -device ide-hd,drive=d0,secs=1,cyls=1,heads=1    2>/dev/null -accel qtest
>> ----------------------------------- stderr -----------------------------------
>> warning: fd: migration to a file is deprecated. Use file: instead.
>> warning: fd: migration to a file is deprecated. Use file: instead.
>> ../tests/qtest/libqtest.c:205: kill_qemu() detected QEMU death from signal 11 (Segmentation fault) (core dumped)
>>
>> *** /ppc64/migration/multifd/tcp/plain/cancel, qtest-ppc64 on i686 host
>>
>> https://gitlab.com/qemu-project/qemu/-/jobs/7786579152
>>
>> 174/315 qemu:qtest+qtest-ppc64 / qtest-ppc64/migration-test                       ERROR          381.00s   killed by signal 6 SIGABRT
>>>>> PYTHON=/builds/qemu-project/qemu/build/pyvenv/bin/python3 QTEST_QEMU_IMG=./qemu-img G_TEST_DBUS_DAEMON=/builds/qemu-project/qemu/tests/dbus-vmstate-daemon.sh QTEST_QEMU_BINARY=./qemu-system-ppc64 MALLOC_PERTURB_=178 QTEST_QEMU_STORAGE_DAEMON_BINARY=./storage-daemon/qemu-storage-daemon /builds/qemu-project/qemu/build/tests/qtest/migration-test --tap -k
>> ――――――――――――――――――――――――――――――――――――― ✀  ―――――――――――――――――――――――――――――――――――――
>> stderr:
>> qemu-system-ppc64: Cannot read from TLS channel: The TLS connection was non-properly terminated.
>> warning: fd: migration to a file is deprecated. Use file: instead.
>> warning: fd: migration to a file is deprecated. Use file: instead.
>> ../tests/qtest/libqtest.c:205: kill_qemu() detected QEMU death from signal 11 (Segmentation fault) (core dumped)
>> (test program exited with status code -6)
>> TAP parsing error: Too few tests run (expected 61, got 47)
>> ――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――
>>
>> # Start of plain tests
>> # Running /ppc64/migration/multifd/tcp/plain/cancel
>> # Using machine type: pseries-9.2
>> # starting QEMU: exec ./qemu-system-ppc64 -qtest unix:/tmp/qtest-40766.sock -qtest-log /dev/null -chardev socket,path=/tmp/qtest-40766.qmp,id=char0 -mon chardev=char0,mode=control -display none -audio none -accel kvm -accel tcg -machine pseries-9.2,vsmt=8 -name source,debug-threads=on -m 256M -serial file:/tmp/migration-test-H0Z1T2/src_serial -nodefaults -machine cap-cfpc=broken,cap-sbbc=broken,cap-ibs=broken,cap-ccf-assist=off, -bios /tmp/migration-test-H0Z1T2/bootsect    2>/dev/null -accel qtest
>> # starting QEMU: exec ./qemu-system-ppc64 -qtest unix:/tmp/qtest-40766.sock -qtest-log /dev/null -chardev socket,path=/tmp/qtest-40766.qmp,id=char0 -mon chardev=char0,mode=control -display none -audio none -accel kvm -accel tcg -machine pseries-9.2,vsmt=8 -name target,debug-threads=on -m 256M -serial file:/tmp/migration-test-H0Z1T2/dest_serial -incoming defer -nodefaults -machine cap-cfpc=broken,cap-sbbc=broken,cap-ibs=broken,cap-ccf-assist=off, -bios /tmp/migration-test-H0Z1T2/bootsect    2>/dev/null -accel qtest
>> ----------------------------------- stderr -----------------------------------
>> qemu-system-ppc64: Cannot read from TLS channel: The TLS connection was non-properly terminated.
>> warning: fd: migration to a file is deprecated. Use file: instead.
>> warning: fd: migration to a file is deprecated. Use file: instead.
>> ../tests/qtest/libqtest.c:205: kill_qemu() detected QEMU death from signal 11 (Segmentation fault) (core dumped)
>>
>> (test program exited with status code -6)
>> =================================8<================================
>>
>> So.. it's the same test (multifd/tcp/plain/cancel) that is failing on
>> different host / arch being tested.  What is more weird is the two failures
>> are different, the 2nd failure throw out a TLS error even though the test
>> doesn't yet have tls involved.
>
> I think that's just a parallel test being cancelled prematurely, either
> due to the crash or due to the timeout.
>
>>
>> Fabiano, is this the issue you're looking at?
>
> Yes. I can reproduce locally by running 2 processes in parallel: 1 loop
> with make -j$(nproc) check and another loop with tcp/plain/cancel. It
> takes ~1h to hit. I've seen crashes with ppc64, s390 and
> aarch64.
>

Ok, the issue is that after commit 5ef7e26bdb ("migration/multifd: solve
zero page causing multiple page faults"), the multifd code started using
the rb->receivedmap bitmap, which belongs to the ram code and is
initialized and *freed* from the ram SaveVMHandlers.

process_incoming_migration_co()        ...
  qemu_loadvm_state()                  multifd_nocomp_recv()
    qemu_loadvm_state_cleanup()          ramblock_recv_bitmap_set_offset()
      rb->receivedmap = NULL               set_bit_atomic(..., rb->receivedmap)
  ...
  migration_incoming_state_destroy()
    multifd_recv_cleanup()
      multifd_recv_terminate_threads(NULL)

Multifd threads are live until migration_incoming_state_destroy(), which
is called some time later.

>> Peter, do you think it'll be helpful if we temporarily mark this test as
>> "slow" too so it's not run in CI (so we still run it ourselves when prepare
>> migration PR, with the hope that it can reproduce)?
>>
>> Thanks,