Re: [Qemu-devel] [PULL 1/1] kvm-all: Partially reverts 4fe6d78b2e to remove the cleanup call

[Paolo Bonzini <pbonzini@redhat.com>]

On 24/01/2018 10:34, Greg Kurz wrote:
> On Wed, 24 Jan 2018 10:14:57 +0100
> Paolo Bonzini <pbonzini@redhat.com> wrote:
> 
>> On 24/01/2018 10:05, Greg Kurz wrote:
>>> On Wed, 24 Jan 2018 09:46:21 +0100
>>> Greg Kurz <groug@kaod.org> wrote:
>>>   
>>>> Please note that Peter usually doesn't work on Wednesdays. The master branch
>>>> might remain broken for everyone until tomorrow... :-\
>>>>
>>>> And I don't think this is the right fix anyway. See below.
>>>>
>>>> On Wed, 24 Jan 2018 00:44:14 +0200
>>>> "Michael S. Tsirkin" <mst@redhat.com> wrote:
>>>>  
>>>>> From: Jose Ricardo Ziviani <joserz@linux.vnet.ibm.com>
>>>>>
>>>>> This commit partially reverts the commit 4fe6d78b2e because of issues
>>>>> reported in the virtio.
>>>>>
>>>>> Examples:
>>>>>
>>>>> $ qemu-system-ppc64 -cpu POWER8 -nographic -vga none -m 4G \
>>>>>   -M pseries,accel=kvm -netdev type=user,id=net0 \
>>>>>   -device virtio-net-pci,netdev=net0 -drive file=../disk.qcow2,if=virtio
>>>>>
>>>>> Populating /vdevice/nvram@71000001
>>>>> Populating /vdevice/v-scsi@71000002
>>>>>        SCSI: Looking for devices
>>>>>           8200000000000000 CD-ROM   : "QEMU     QEMU CD-ROM      2.5+"
>>>>> Populating /pci@800000020000000
>>>>>                      00 0000 (D) : 1af4 1000    virtio [ net ]
>>>>> Aborted
>>>>>
>>>>> $ qemu-system-x86_64 -m 4G -enable-kvm -drive file=util.qcow2,if=virtio
>>>>>
>>>>> Running QEMU with GTK 2.x is deprecated, and will be removed
>>>>> in a future release. Please switch to GTK 3.x instead
>>>>> [1]    5282 abort
>>>>>
>>>>> Reference http://lists.nongnu.org/archive/html/qemu-devel/2018-01/msg05457.html
>>>>>
>>>>> Reported-by: Anton Blanchard <anton@samba.org>
>>>>> Signed-off-by: Jose Ricardo Ziviani <joserz@linux.vnet.ibm.com>
>>>>> Reviewed-by: Daniel Henrique Barboza <danielhb@linux.vnet.ibm.com>
>>>>> Tested-by: Daniel Henrique Barboza <danielhb@linux.vnet.ibm.com>
>>>>> Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
>>>>> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
>>>>> ---
>>>>>  accel/kvm/kvm-all.c | 4 ----
>>>>>  1 file changed, 4 deletions(-)
>>>>>
>>>>> diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
>>>>> index 071f4f5..f290f48 100644
>>>>> --- a/accel/kvm/kvm-all.c
>>>>> +++ b/accel/kvm/kvm-all.c
>>>>> @@ -812,10 +812,6 @@ static void kvm_mem_ioeventfd_del(MemoryListener *listener,
>>>>>      if (r < 0) {
>>>>>          abort();
>>>>>      }
>>>>> -
>>>>> -    if (e->cleanup) {
>>>>> -        e->cleanup(e);
>>>>> -    }    
>>>>
>>>> This looks wrong as the cleanup is expected to do things like closing fds:
>>>>
>>>> static void virtio_bus_cleanup_event_notifier(EventNotifier *notifier)
>>>> {
>>>>     /* Test and clear notifier after disabling event,
>>>>      * in case poll callback didn't have time to run.
>>>>      */
>>>>     virtio_queue_host_notifier_read(notifier);
>>>>     event_notifier_cleanup(notifier);
>>>> }
>>>>
>>>> void event_notifier_cleanup(EventNotifier *e)
>>>> {
>>>>     if (e->rfd != e->wfd) {
>>>>         close(e->rfd);
>>>>     }
>>>>     close(e->wfd);
>>>>     e->rfd = -1;
>>>>     e->wfd = -1;
>>>>     e->cleanup = NULL;
>>>> }
>>>>
>>>> And indeed, with this patch applied, QEMU leaks eventfds on every machine
>>>> reset.
>>>>  
>>>
>>> Reverting 4fe6d78b2e entirely isn't even enough and QEMU aborts at the
>>> next machine reset. The following commit must be reverted as well:
>>>
>>> commit 6f0bb230722931d17fb284eee8efd40b9d653822
>>> Author: Gal Hammer <ghammer@redhat.com>
>>> Date:   Sun Jan 14 12:06:56 2018 +0200
>>>
>>>     virtio: improve virtio devices initialization time  
>>
>> I'm a bit confused by this patch.  The basic idea of wrapping with
>> transaction_begin/commit is clear (without it you have quadratic
>> behavior from removing one ioeventfd at a time), but I don't understand
>> why the new ->cleanup member is needed.
> 
> I don't understand either... the cover letter of the series says:
> 
> "The patch wraps all the changes made to the Memory Regions during the
> eventfd registrations in a memory regions transaction. I had to add a
> cleanup callback function to the EventNotifier struct, so it will be
> possible to use a transaction in the shutdown code path as well."
> 
> Until this is sorted out, maybe best to revert both commits or even
> the full series (ie, f87d72f5c5bf as well), no ?

Yes, indeed.

Paolo