Re: [PULL 30/33] migration: do not restart VM after successful snapshot-load

[Paolo Bonzini <pbonzini@redhat.com>]

On 11/05/21 10:56, Dr. David Alan Gilbert wrote:
> * Paolo Bonzini (pbonzini@redhat.com) wrote:
>> The HMP loadvm code is calling load_snapshot rather than
>> qmp_snapshot_load, in order to bypass the job infrastructure.  The code
>> around it is almost the same, with one difference: hmp_loadvm is
>> restarting the VM if load_snapshot fails, qmp_snapshot_load is doing so
>> if load_snapshot succeeds.
>>
>> Fix the bug in QMP by moving the common code to load_snapshot.
> 
> See my comment:
> https://lists.gnu.org/archive/html/qemu-devel/2021-05/msg01103.html
> 
> but you've also lost Eric's Rb.

Sorry, I missed both replies.  As Daniel pointed out, the bug is in the 
QMP version.  Kevin has the correct fix, I'll send the cleanup of 
vm_stop/vm_start separately on top of his patch.

Paolo

> Dave
> 
>> Cc: qemu-stable@nongnu.org
>> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
>> ---
>>   migration/savevm.c | 16 ++++++++--------
>>   monitor/hmp-cmds.c |  7 +------
>>   2 files changed, 9 insertions(+), 14 deletions(-)
>>
>> diff --git a/migration/savevm.c b/migration/savevm.c
>> index 52e2d72e4b..a899191cbf 100644
>> --- a/migration/savevm.c
>> +++ b/migration/savevm.c
>> @@ -2992,6 +2992,7 @@ bool load_snapshot(const char *name, const char *vmstate,
>>       int ret;
>>       AioContext *aio_context;
>>       MigrationIncomingState *mis = migration_incoming_get_current();
>> +    int saved_vm_running  = runstate_is_running();
>>   
>>       if (!bdrv_all_can_snapshot(has_devices, devices, errp)) {
>>           return false;
>> @@ -3024,6 +3025,8 @@ bool load_snapshot(const char *name, const char *vmstate,
>>           return false;
>>       }
>>   
>> +    vm_stop(RUN_STATE_RESTORE_VM);
>> +
>>       /*
>>        * Flush the record/replay queue. Now the VM state is going
>>        * to change. Therefore we don't need to preserve its consistency
>> @@ -3061,13 +3064,17 @@ bool load_snapshot(const char *name, const char *vmstate,
>>   
>>       if (ret < 0) {
>>           error_setg(errp, "Error %d while loading VM state", ret);
>> -        return false;
>> +        goto err_restart;
>>       }
>>   
>>       return true;
>>   
>>   err_drain:
>>       bdrv_drain_all_end();
>> +err_restart:
>> +    if (saved_vm_running) {
>> +        vm_start();
>> +    }
>>       return false;
>>   }
>>   
>> @@ -3135,17 +3142,10 @@ static void snapshot_load_job_bh(void *opaque)
>>   {
>>       Job *job = opaque;
>>       SnapshotJob *s = container_of(job, SnapshotJob, common);
>> -    int orig_vm_running;
>>   
>>       job_progress_set_remaining(&s->common, 1);
>>   
>> -    orig_vm_running = runstate_is_running();
>> -    vm_stop(RUN_STATE_RESTORE_VM);
>> -
>>       s->ret = load_snapshot(s->tag, s->vmstate, true, s->devices, s->errp);
>> -    if (s->ret && orig_vm_running) {
>> -        vm_start();
>> -    }
>>   
>>       job_progress_update(&s->common, 1);
>>   
>> diff --git a/monitor/hmp-cmds.c b/monitor/hmp-cmds.c
>> index 0ad5b77477..a39436c8cb 100644
>> --- a/monitor/hmp-cmds.c
>> +++ b/monitor/hmp-cmds.c
>> @@ -1127,15 +1127,10 @@ void hmp_balloon(Monitor *mon, const QDict *qdict)
>>   
>>   void hmp_loadvm(Monitor *mon, const QDict *qdict)
>>   {
>> -    int saved_vm_running  = runstate_is_running();
>>       const char *name = qdict_get_str(qdict, "name");
>>       Error *err = NULL;
>>   
>> -    vm_stop(RUN_STATE_RESTORE_VM);
>> -
>> -    if (!load_snapshot(name, NULL, false, NULL, &err) && saved_vm_running) {
>> -        vm_start();
>> -    }
>> +    load_snapshot(name, NULL, false, NULL, &err);
>>       hmp_handle_error(mon, err);
>>   }
>>   
>> -- 
>> 2.26.2
>>
>>
>>