Re: [Qemu-devel] [PATCH 2/3] virtio: postpone the execution of event_notifier_cleanup function

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, Jan 22, 2018 at 06:35:03PM +0100, Marc-André Lureau wrote:
> Hi
> 
> On Mon, Jan 22, 2018 at 12:53 PM, Michal Privoznik <mprivozn@redhat.com> wrote:
> > On 01/14/2018 11:06 AM, Gal Hammer wrote:
> >> Use the EventNotifier's cleanup callback function to execute the
> >> event_notifier_cleanup function after kvm unregistered the eventfd.
> >>
> >> This change supports running the virtio_bus_set_host_notifier
> >> function inside a memory region transaction. Otherwise, a closed
> >> fd is sent to kvm, which results in a failure.
> >>
> >> Signed-off-by: Gal Hammer <ghammer@redhat.com>
> >> ---
> >>  accel/kvm/kvm-all.c    |  4 ++++
> >>  hw/virtio/virtio-bus.c | 19 +++++++++++--------
> >>  2 files changed, 15 insertions(+), 8 deletions(-)
> >>
> >> diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
> >> index f290f48..071f4f5 100644
> >> --- a/accel/kvm/kvm-all.c
> >> +++ b/accel/kvm/kvm-all.c
> >> @@ -812,6 +812,10 @@ static void kvm_mem_ioeventfd_del(MemoryListener *listener,
> >>      if (r < 0) {
> >>          abort();
> >>      }
> >> +
> >> +    if (e->cleanup) {
> >> +        e->cleanup(e);
> >> +    }
> >>  }
> >>
> >>  static void kvm_io_ioeventfd_add(MemoryListener *listener,
> >> diff --git a/hw/virtio/virtio-bus.c b/hw/virtio/virtio-bus.c
> >> index 3042232..8106346 100644
> >> --- a/hw/virtio/virtio-bus.c
> >> +++ b/hw/virtio/virtio-bus.c
> >> @@ -256,6 +256,15 @@ bool virtio_bus_ioeventfd_enabled(VirtioBusState *bus)
> >>      return k->ioeventfd_assign && k->ioeventfd_enabled(proxy);
> >>  }
> >>
> >> +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);
> >> +}
> >> +
> >>  /*
> >>   * This function switches ioeventfd on/off in the device.
> >>   * The caller must set or clear the handlers for the EventNotifier.
> >> @@ -283,19 +292,13 @@ int virtio_bus_set_host_notifier(VirtioBusState *bus, int n, bool assign)
> >>          r = k->ioeventfd_assign(proxy, notifier, n, true);
> >>          if (r < 0) {
> >>              error_report("%s: unable to assign ioeventfd: %d", __func__, r);
> >> -            goto cleanup_event_notifier;
> >> +            virtio_bus_cleanup_event_notifier(notifier);
> >>          }
> >> -        return 0;
> >>      } else {
> >> +        notifier->cleanup = virtio_bus_cleanup_event_notifier;
> >>          k->ioeventfd_assign(proxy, notifier, n, false);
> >>      }
> >>
> >> -cleanup_event_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);
> >>      return r;
> >>  }
> >>
> >>
> >
> > This causes abort() to me:
> >
> > Thread 7 "CPU 3/KVM" received signal SIGABRT, Aborted.
> > [Switching to Thread 0x7f78fa1f4700 (LWP 13737)]
> > __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:51
> > 51      }
> > __GI_raise 7 # bt
> > #0  __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:51
> > #1  0x00007f7a09ff5c1a in __GI_abort () at abort.c:89
> > #2  0x000055f2a70bce9d in kvm_io_ioeventfd_del (listener=0x55f2a7d19200 <kvm_io_listener>, section=0x7f78fa1f10f0, match_data=true, data=0, e=0x7f79fc81f080) at /home/zippy/work/qemu/qemu.git/accel/kvm/kvm-all.c:852
> > #3  0x000055f2a70a6fac in address_space_add_del_ioeventfds (as=0x55f2a7e86620 <address_space_io>, fds_new=0x7f78e40b9e80, fds_new_nb=2, fds_old=0x7f78e40b9f10, fds_old_nb=3) at /home/zippy/work/qemu/qemu.git/memory.c:832
> > #4  0x000055f2a70a744d in address_space_update_ioeventfds (as=0x55f2a7e86620 <address_space_io>) at /home/zippy/work/qemu/qemu.git/memory.c:895
> > #5  0x000055f2a70a7f04 in memory_region_transaction_commit () at /home/zippy/work/qemu/qemu.git/memory.c:1097
> > #6  0x000055f2a70ab0d1 in memory_region_del_eventfd (mr=0x55f2a9422250, addr=16, size=2, match_data=true, data=0, e=0x7f79fc81f080) at /home/zippy/work/qemu/qemu.git/memory.c:2273
> > #7  0x000055f2a7411f18 in virtio_pci_ioeventfd_assign (d=0x55f2a9421970, notifier=0x7f79fc81f080, n=0, assign=false) at hw/virtio/virtio-pci.c:280
> > #8  0x000055f2a7418e6f in virtio_bus_set_host_notifier (bus=0x55f2a9429a68, n=0, assign=false) at hw/virtio/virtio-bus.c:299
> > #9  0x000055f2a710236a in virtio_scsi_dataplane_stop (vdev=0x55f2a9429ae0) at /home/zippy/work/qemu/qemu.git/hw/scsi/virtio-scsi-dataplane.c:215
> > #10 0x000055f2a7418bb3 in virtio_bus_stop_ioeventfd (bus=0x55f2a9429a68) at hw/virtio/virtio-bus.c:246
> > #11 0x000055f2a7411f63 in virtio_pci_stop_ioeventfd (proxy=0x55f2a9421970) at hw/virtio/virtio-pci.c:294
> > #12 0x000055f2a74144ab in virtio_pci_common_write (opaque=0x55f2a9421970, addr=20, val=0, size=1) at hw/virtio/virtio-pci.c:1262
> > #13 0x000055f2a70a6016 in memory_region_write_accessor (mr=0x55f2a9422340, addr=20, value=0x7f78fa1f1558, size=1, shift=0, mask=255, attrs=...) at /home/zippy/work/qemu/qemu.git/memory.c:560
> > #14 0x000055f2a70a622e in access_with_adjusted_size (addr=20, value=0x7f78fa1f1558, size=1, access_size_min=1, access_size_max=4, access_fn=0x55f2a70a5f2c <memory_region_write_accessor>, mr=0x55f2a9422340, attrs=...) at /home/zippy/work/qemu/qemu.git/memory.c:627
> > #15 0x000055f2a70a8eb0 in memory_region_dispatch_write (mr=0x55f2a9422340, addr=20, data=0, size=1, attrs=...) at /home/zippy/work/qemu/qemu.git/memory.c:1503
> > #16 0x000055f2a7058b2b in flatview_write_continue (fv=0x7f78e405eba0, addr=4269834260, attrs=..., buf=0x7f7a26c36028 "", len=1, addr1=20, l=1, mr=0x55f2a9422340) at /home/zippy/work/qemu/qemu.git/exec.c:3038
> > #17 0x000055f2a7058c79 in flatview_write (fv=0x7f78e405eba0, addr=4269834260, attrs=..., buf=0x7f7a26c36028 "", len=1) at /home/zippy/work/qemu/qemu.git/exec.c:3083
> > #18 0x000055f2a7059050 in flatview_rw (fv=0x7f78e405eba0, addr=4269834260, attrs=..., buf=0x7f7a26c36028 "", len=1, is_write=true) at /home/zippy/work/qemu/qemu.git/exec.c:3192
> > #19 0x000055f2a7059108 in address_space_rw (as=0x55f2a7e86680 <address_space_memory>, addr=4269834260, attrs=..., buf=0x7f7a26c36028 "", len=1, is_write=true) at /home/zippy/work/qemu/qemu.git/exec.c:3202
> > #20 0x000055f2a70bf42c in kvm_cpu_exec (cpu=0x55f2a850cda0) at /home/zippy/work/qemu/qemu.git/accel/kvm/kvm-all.c:1941
> > #21 0x000055f2a708d455 in qemu_kvm_cpu_thread_fn (arg=0x55f2a850cda0) at /home/zippy/work/qemu/qemu.git/cpus.c:1196
> > #22 0x000055f2a75ce829 in qemu_thread_start (args=0x55f2a852e260) at util/qemu-thread-posix.c:504
> > #23 0x00007f7a0a375887 in start_thread (arg=0x7f78fa1f4700) at pthread_create.c:456
> > #24 0x00007f7a0a0b7d4f in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:97
> > __GI_raise 7 # up
> > #1  0x00007f7a09ff5c1a in __GI_abort () at abort.c:89
> > 89            raise (SIGABRT);
> > __GI_abort 7 #
> > #2  0x000055f2a70bce9d in kvm_io_ioeventfd_del (listener=0x55f2a7d19200 <kvm_io_listener>, section=0x7f78fa1f10f0, match_data=true, data=0, e=0x7f79fc81f080) at /home/zippy/work/qemu/qemu.git/accel/kvm/kvm-all.c:852
> > 852             abort();
> > kvm_io_ioeventfd_del 7 # p *e
> > $1 = {rfd = -1, wfd = -1, cleanup = 0x0}
> >
> >
> > I think the problem is that event_notifier_cleanup() is called before
> > kvm_io_ioeventfd_del() and both are called over the same EventNotifier.
> > This is supported by another data I was able to collect in a different
> > run:
> >
> > Thread 4 "CPU 0/KVM" hit Breakpoint 1, event_notifier_cleanup (e=0x7fc6ac26f080) at util/event_notifier-posix.c:83
> > 83          if (e->rfd != e->wfd) {
> > event_notifier_cleanup 4 # p *e
> > $1 = {rfd = 48, wfd = 48, cleanup = 0x55c91c76ac87 <virtio_bus_cleanup_event_notifier>}
> > event_notifier_cleanup 4 # c
> > Continuing.
> >
> > Thread 4 "CPU 0/KVM" received signal SIGABRT, Aborted.
> > __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:51
> > 51      }
> > __GI_raise 4 # up
> > #1  0x00007fc6b9a45c1a in __GI_abort () at abort.c:89
> > 89            raise (SIGABRT);
> > __GI_abort 4 #
> > #2  0x000055c91c40ee9d in kvm_io_ioeventfd_del (listener=0x55c91d06b200 <kvm_io_listener>, section=0x7fc5ab1fa0f0, match_data=true, data=0, e=0x7fc6ac26f080) at /home/zippy/work/qemu/qemu.git/accel/kvm/kvm-all.c:852
> > 852             abort();
> > kvm_io_ioeventfd_del 4 # p *e
> > $2 = {rfd = -1, wfd = -1, cleanup = 0x0}
> >
> >
> > So I drafted dirty workaround:
> >
> > index 071f4f57c0..bf15344533 100644
> > --- i/accel/kvm/kvm-all.c
> > +++ w/accel/kvm/kvm-all.c
> > @@ -845,6 +845,9 @@ static void kvm_io_ioeventfd_del(MemoryListener *listener,
> >      int fd = event_notifier_get_fd(e);
> >      int r;
> >
> > +    if (fd == -1)
> > +        return;
> > +
> >      r = kvm_set_ioeventfd_pio(fd, section->offset_within_address_space,
> >                                data, false, int128_get64(section->size),
> >                                match_data);
> >
> > But this time I'm getting following error:
> >
> > kvm_io_ioeventfd_add: error adding ioeventfd: File exists
> >
> > __GI_raise 7 # up
> > #1  0x00007f3ccd579c1a in __GI_abort () at abort.c:89
> > 89            raise (SIGABRT);
> > __GI_abort 7 #
> > #2  0x000055c68ac84e08 in kvm_io_ioeventfd_add (listener=0x55c68b8e1200 <kvm_io_listener>, section=0x7f3bbd7f1090, match_data=true, data=0, e=0x7f3bbcf8d080) at /home/zippy/work/qemu/qemu.git/accel/kvm/kvm-all.c:835
> > 835             abort();
> > kvm_io_ioeventfd_add 7 # p *e
> > $1 = {rfd = 48, wfd = 48, cleanup = 0x0}
> >
> 
> I was about to report the same error when booting an uefi guest, I
> bisected down to the same first bad commit.
> 
> Thanks Michal

Gal - any input on this before I revert?

> -- 
> Marc-André Lureau