Re: [Qemu-devel] [PATCH] qdev: free qemu-opts when the QOM path goes away

[Andreas Färber]

Am 05.11.2015 um 13:47 schrieb Markus Armbruster:
> Paolo Bonzini <address@hidden> writes:
>> On 05/11/2015 13:06, Andreas Färber wrote:
>>>> 1. Wouldn't it be cleaner to delete dev-opts *before* sending
>>>>    DEVICE_DELETED?  Like this:
>>>>
>>>>     +++ b/hw/core/qdev.c
>>>>     @@ -1244,6 +1244,9 @@ static void device_unparent(Object *obj)
>>>>              dev->parent_bus = NULL;
>>>>          }
>>>>
>>>>     +    qemu_opts_del(dev->opts);
>>>>     +    dev->opts = NULL;
>>>>     +
>>>>          /* Only send event if the device had been completely realized */
>>>>          if (dev->pending_deleted_event) {
>>>>              gchar *path = object_get_canonical_path(OBJECT(dev));
>>>
>>> To me this proposal sounds sane, but I did not get to tracing the code
>>> flow here. Paolo, which approach do you prefer and why?
>>
>> It doesn't really matter, because the BQL is being held here.
>>
>> On the other hand, if the opts are deleted in finalize, there is an
>> arbitrary delay because finalize is typically called after a
>> synchronize_rcu period.
>>
>>>>> 2. If the device is a block device, then unplugging it also deletes its
>>>>>    backend (ugly wart we keep for backward compatibility; *not* for
>>>>>    blockdev-add, though).  This backend also has a QemuOpts.  It gets
>>>>>    deleted in drive_info_del().  Just like device_finalize(), it runs
>>>>>    within object_unref(), i.e. after DEVICE_DELETED is sent.  Same race,
>>>>>    different ID, or am I missing something?
>>>>>
>>>>>    See also https://bugzilla.redhat.com/show_bug.cgi?id=1256044
>>>
>>> If we can leave this patch decoupled from block layer and decide soonish
>>> on the desired approach, I'd be happy to include it in my upcoming
>>> qom-devices pull.
>>
>> I agree with you, the block layer bug is separate.
> 
> Related, but clearly separate.  Mentioning it in the commit message
> would be nice, though.

Paolo, pong: I gathered that I should queue the original patch without
Markus's proposed change, correct? And do you want to add some sentence
to the commit message as requested by Markus?

Regards,
Andreas

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