Re: [PATCH v1 5/9] hw/virtio: introduce virtio_device_should_start

[Christian Borntraeger <borntraeger@linux.ibm.com>]

Am 14.11.22 um 18:20 schrieb Michael S. Tsirkin:
> On Mon, Nov 14, 2022 at 06:15:30PM +0100, Christian Borntraeger wrote:
>>
>>
>> Am 14.11.22 um 18:10 schrieb Michael S. Tsirkin:
>>> On Mon, Nov 14, 2022 at 05:55:09PM +0100, Christian Borntraeger wrote:
>>>>
>>>>
>>>> Am 14.11.22 um 17:37 schrieb Michael S. Tsirkin:
>>>>> On Mon, Nov 14, 2022 at 05:18:53PM +0100, Christian Borntraeger wrote:
>>>>>> Am 08.11.22 um 10:23 schrieb Alex Bennée:
>>>>>>> The previous fix to virtio_device_started revealed a problem in its
>>>>>>> use by both the core and the device code. The core code should be able
>>>>>>> to handle the device "starting" while the VM isn't running to handle
>>>>>>> the restoration of migration state. To solve this dual use introduce a
>>>>>>> new helper for use by the vhost-user backends who all use it to feed a
>>>>>>> should_start variable.
>>>>>>>
>>>>>>> We can also pick up a change vhost_user_blk_set_status while we are at
>>>>>>> it which follows the same pattern.
>>>>>>>
>>>>>>> Fixes: 9f6bcfd99f (hw/virtio: move vm_running check to virtio_device_started)
>>>>>>> Fixes: 27ba7b027f (hw/virtio: add boilerplate for vhost-user-gpio device)
>>>>>>> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
>>>>>>> Cc: "Michael S. Tsirkin" <mst@redhat.com>
>>>>>>
>>>>>> Hmmm, is this
>>>>>> commit 259d69c00b67c02a67f3bdbeeea71c2c0af76c35
>>>>>> Author:     Alex Bennée <alex.bennee@linaro.org>
>>>>>> AuthorDate: Mon Nov 7 12:14:07 2022 +0000
>>>>>> Commit:     Michael S. Tsirkin <mst@redhat.com>
>>>>>> CommitDate: Mon Nov 7 14:08:18 2022 -0500
>>>>>>
>>>>>>        hw/virtio: introduce virtio_device_should_start
>>>>>>
>>>>>> and older version?
>>>>>
>>>>> This is what got merged:
>>>>> https://lore.kernel.org/r/20221107121407.1010913-1-alex.bennee%40linaro.org
>>>>> This patch was sent after I merged the RFC.
>>>>> I think the only difference is the commit log but I might be missing
>>>>> something.
>>>>>
>>>>>> This does not seem to fix the regression that I have reported.
>>>>>
>>>>> This was applied on top of 9f6bcfd99f which IIUC does, right?
>>>>>
>>>>>
>>>>
>>>> QEMU master still fails for me for suspend/resume to disk:
>>>>
>>>> #0  0x000003ff8e3980a6 in __pthread_kill_implementation () at /lib64/libc.so.6
>>>> #1  0x000003ff8e348580 in raise () at /lib64/libc.so.6
>>>> #2  0x000003ff8e32b5c0 in abort () at /lib64/libc.so.6
>>>> #3  0x000003ff8e3409da in __assert_fail_base () at /lib64/libc.so.6
>>>> #4  0x000003ff8e340a4e in  () at /lib64/libc.so.6
>>>> #5  0x000002aa1ffa8966 in vhost_vsock_common_pre_save (opaque=<optimized out>) at ../hw/virtio/vhost-vsock-common.c:203
>>>> #6  0x000002aa1fe5e0ee in vmstate_save_state_v
>>>>       (f=f@entry=0x2aa21bdc170, vmsd=0x2aa204ac5f0 <vmstate_virtio_vhost_vsock>, opaque=0x2aa21bac9f8, vmdesc=vmdesc@entry=0x3fddc08eb30, version_id=version_id@entry=0) at ../migration/vmstate.c:329
>>>> #7  0x000002aa1fe5ebf8 in vmstate_save_state (f=f@entry=0x2aa21bdc170, vmsd=<optimized out>, opaque=<optimized out>, vmdesc_id=vmdesc_id@entry=0x3fddc08eb30) at ../migration/vmstate.c:317
>>>> #8  0x000002aa1fe75bd0 in vmstate_save (f=f@entry=0x2aa21bdc170, se=se@entry=0x2aa21bdbe90, vmdesc=vmdesc@entry=0x3fddc08eb30) at ../migration/savevm.c:908
>>>> #9  0x000002aa1fe79584 in qemu_savevm_state_complete_precopy_non_iterable (f=f@entry=0x2aa21bdc170, in_postcopy=in_postcopy@entry=false, inactivate_disks=inactivate_disks@entry=true)
>>>>       at ../migration/savevm.c:1393
>>>> #10 0x000002aa1fe79a96 in qemu_savevm_state_complete_precopy (f=0x2aa21bdc170, iterable_only=iterable_only@entry=false, inactivate_disks=inactivate_disks@entry=true) at ../migration/savevm.c:1459
>>>> #11 0x000002aa1fe6d6ee in migration_completion (s=0x2aa218ef600) at ../migration/migration.c:3314
>>>> #12 migration_iteration_run (s=0x2aa218ef600) at ../migration/migration.c:3761
>>>> #13 migration_thread (opaque=opaque@entry=0x2aa218ef600) at ../migration/migration.c:3989
>>>> #14 0x000002aa201f0b8c in qemu_thread_start (args=<optimized out>) at ../util/qemu-thread-posix.c:505
>>>> #15 0x000003ff8e396248 in start_thread () at /lib64/libc.so.6
>>>> #16 0x000003ff8e41183e in thread_start () at /lib64/libc.so.6
>>>>
>>>> Michael, your previous branch did work if I recall correctly.
>>>
>>> That one was failing under github CI though (for reasons we didn't
>>> really address, such as disconnect during stop causing a recursive
>>> call to stop, but there you are).
>> Even the double revert of everything?
> 
> I don't remember at this point.
> 
>> So how do we proceed now?
> 
> I'm hopeful Alex will come up with a fix.


The initial fix changed to qemu/master does still work for me

diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
index a973811cbfc6..fb3072838119 100644
--- a/include/hw/virtio/virtio.h
+++ b/include/hw/virtio/virtio.h
@@ -411,14 +411,14 @@ static inline bool virtio_device_started(VirtIODevice *vdev, uint8_t status)
   */
  static inline bool virtio_device_should_start(VirtIODevice *vdev, uint8_t status)
  {
-    if (vdev->use_started) {
-        return vdev->started;
-    }
-
      if (!vdev->vm_running) {
          return false;
      }
  
+    if (vdev->use_started) {
+        return vdev->started;
+    }
+
      return status & VIRTIO_CONFIG_S_DRIVER_OK;
  }