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

[Marcelo Tosatti <mtosatti@redhat.com>]

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);