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

[Greg Kurz <groug@kaod.org>]

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 ?

> Paolo