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

[Andrey Korolyov]

On Wed, Jul 16, 2014 at 5:16 AM, Marcelo Tosatti <address@hidden> wrote:
> On Wed, Jul 16, 2014 at 03:40:47AM +0400, Andrey Korolyov wrote:
>> On Wed, Jul 16, 2014 at 2:01 AM, Paolo Bonzini <address@hidden> wrote:
>> > Il 15/07/2014 23:25, Andrey Korolyov ha scritto:
>> >
>> >> On Wed, Jul 16, 2014 at 1:09 AM, Marcelo Tosatti <address@hidden>
>> >> 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 <address@hidden>
>> >>>> wrote:
>> >>>>>
>> >>>>> On Tue, Jul 15, 2014 at 9:03 AM, Amit Shah <address@hidden>
>> >>>>> 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 <address@hidden>
>> >>>> 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 <address@hidden>
>> >>>>     Cc: address@hidden
>> >>>>     Signed-off-by: Marcelo Tosatti <address@hidden>
>> >>>>     Signed-off-by: Paolo Bonzini <address@hidden>
>> >>>
>> >>>
>> >>> 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
>>
>> Yes, it solved the issue for me! (it took much time to check because
>> most of country` debian mirrors went inconsistent by some reason)
>>
>> Also trivial addition:
>>
>> diff --git a/migration.c b/migration.c
>> index 34f2325..65d1c88 100644
>> --- a/migration.c
>> +++ b/migration.c
>> @@ -25,6 +25,7 @@
>>  #include "qemu/thread.h"
>>  #include "qmp-commands.h"
>>  #include "trace.h"
>> +#include "sysemu/cpus.h"
>
> And what about not reverting a096b3a6732f846ec57dc28b47ee9435aa0609bf ?
>
> That is, test with a stock qemu.git tree and the patch sent today,
> on this thread, to move cpu_synchronize_all_states ?
>
>

The main reason for things to work for me is a revert of
9b1786829aefb83f37a8f3135e3ea91c56001b56 on top, not adding any other
patches. I had tested two cases, with Alexander`s patch completely
reverted plus suggestion from Marcelo and only with revert 9b178682
plug same suggestion. The difference is that the until Alexander`
patch is not reverted, live migration is always failing by the timeout
value, and when reverted migration always succeeds in 8-10 seconds.
Appropriate diffs are attached for the reference.

diff-with-reverted-agraf-patch.txt
Description: Text document

diff-with-only-late-fix-moved.txt
Description: Text document