Re: [Qemu-devel] latest rc: virtio-blk hangs forever after migration

[Paolo Bonzini <pbonzini@redhat.com>]

Il 15/07/2014 23:25, Andrey Korolyov ha scritto:
> On Wed, Jul 16, 2014 at 1:09 AM, Marcelo Tosatti <mtosatti@redhat.com> wrote:
>> On Tue, Jul 15, 2014 at 06:01:08PM +0400, Andrey Korolyov wrote:
>>> On Tue, Jul 15, 2014 at 10:52 AM, Andrey Korolyov <andrey@xdel.ru> wrote:
>>>> On Tue, Jul 15, 2014 at 9:03 AM, Amit Shah <amit.shah@redhat.com> wrote:
>>>>> On (Sun) 13 Jul 2014 [16:28:56], Andrey Korolyov wrote:
>>>>>> Hello,
>>>>>>
>>>>>> the issue is not specific to the iothread code because generic
>>>>>> virtio-blk also hangs up:
>>>>>
>>>>> Do you know which version works well?  If you could bisect, that'll
>>>>> help a lot.
>>>>>
>>>>> Thanks,
>>>>>                 Amit
>>>>
>>>> Hi,
>>>>
>>>> 2.0 works definitely well. I`ll try to finish bisection today, though
>>>> every step takes about 10 minutes to complete.
>>>
>>> Yay! It is even outside of virtio-blk.
>>>
>>> commit 9b1786829aefb83f37a8f3135e3ea91c56001b56
>>> Author: Marcelo Tosatti <mtosatti@redhat.com>
>>> Date:   Tue Jun 3 13:34:48 2014 -0300
>>>
>>>     kvmclock: Ensure proper env->tsc value for kvmclock_current_nsec calculation
>>>
>>>     Ensure proper env->tsc value for kvmclock_current_nsec calculation.
>>>
>>>     Reported-by: Marcin Gibuła <m.gibula@beyond.pl>
>>>     Cc: qemu-stable@nongnu.org
>>>     Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
>>>     Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
>>
>> Andrey,
>>
>> Can you please provide instructions on how to create reproducible
>> environment?
>>
>> The following patch is equivalent to the original patch, for
>> the purposes of fixing the kvmclock problem.
>>
>> Perhaps it becomes easier to spot the reason for the hang you are
>> experiencing.
>>
>>
>> diff --git a/hw/i386/kvm/clock.c b/hw/i386/kvm/clock.c
>> index 272a88a..feb5fc5 100644
>> --- a/hw/i386/kvm/clock.c
>> +++ b/hw/i386/kvm/clock.c
>> @@ -17,7 +17,6 @@
>>  #include "qemu/host-utils.h"
>>  #include "sysemu/sysemu.h"
>>  #include "sysemu/kvm.h"
>> -#include "sysemu/cpus.h"
>>  #include "hw/sysbus.h"
>>  #include "hw/kvm/clock.h"
>>
>> @@ -66,7 +65,6 @@ static uint64_t kvmclock_current_nsec(KVMClockState *s)
>>
>>      cpu_physical_memory_read(kvmclock_struct_pa, &time, sizeof(time));
>>
>> -    assert(time.tsc_timestamp <= migration_tsc);
>>      delta = migration_tsc - time.tsc_timestamp;
>>      if (time.tsc_shift < 0) {
>>          delta >>= -time.tsc_shift;
>> @@ -125,8 +123,6 @@ static void kvmclock_vm_state_change(void *opaque, int running,
>>          if (s->clock_valid) {
>>              return;
>>          }
>> -
>> -        cpu_synchronize_all_states();
>>          ret = kvm_vm_ioctl(kvm_state, KVM_GET_CLOCK, &data);
>>          if (ret < 0) {
>>              fprintf(stderr, "KVM_GET_CLOCK failed: %s\n", strerror(ret));
>> diff --git a/migration.c b/migration.c
>> index 8d675b3..34f2325 100644
>> --- a/migration.c
>> +++ b/migration.c
>> @@ -608,6 +608,7 @@ static void *migration_thread(void *opaque)
>>                  qemu_system_wakeup_request(QEMU_WAKEUP_REASON_OTHER);
>>                  old_vm_running = runstate_is_running();
>>
>> +                cpu_synchronize_all_states();
>>                  ret = vm_stop_force_state(RUN_STATE_FINISH_MIGRATE);
>>                  if (ret >= 0) {
>>                      qemu_file_set_rate_limit(s->file, INT64_MAX);

It could also be useful to apply the above patch _and_ revert 
a096b3a6732f846ec57dc28b47ee9435aa0609bf, then try to reproduce.

Paolo