Re: [Qemu-devel] [PATCH v3 1/1] migration: disallow migrate_add_blocker during migration

[Dr. David Alan Gilbert]

* Greg Kurz (address@hidden) wrote:
> On Fri,  9 Dec 2016 12:25:47 -0500
> John Snow <address@hidden> wrote:
> 
> > If a migration is already in progress and somebody attempts
> > to add a migration blocker, this should rightly fail.
> > 
> > Add an errp parameter and a retcode return value to migrate_add_blocker.
> > 
> > Signed-off-by: John Snow <address@hidden>
> > ---
> >  block/qcow.c                  |  6 +++++-
> >  block/vdi.c                   |  6 +++++-
> >  block/vhdx.c                  | 24 ++++++++++++++----------
> >  block/vmdk.c                  |  7 ++++++-
> >  block/vpc.c                   | 10 +++++++---
> >  block/vvfat.c                 | 20 ++++++++++++--------
> >  hw/9pfs/9p.c                  | 16 ++++++++++++----
> >  hw/display/virtio-gpu.c       | 29 ++++++++++++++++-------------
> >  hw/misc/ivshmem.c             | 11 +++++++----
> >  hw/scsi/vhost-scsi.c          | 25 +++++++++++++++++++------
> >  hw/virtio/vhost.c             |  8 +++++++-
> >  include/migration/migration.h |  6 +++++-
> >  migration/migration.c         | 35 +++++++++++++++++++++++++++++++++--
> >  stubs/migr-blocker.c          |  3 ++-
> >  target-i386/kvm.c             | 16 +++++++++++++---
> >  15 files changed, 163 insertions(+), 59 deletions(-)
> > 
> > diff --git a/block/qcow.c b/block/qcow.c
> > index 7540f43..11526a1 100644
> > --- a/block/qcow.c
> > +++ b/block/qcow.c
> > @@ -252,7 +252,11 @@ static int qcow_open(BlockDriverState *bs, QDict 
> > *options, int flags,
> >      error_setg(&s->migration_blocker, "The qcow format used by node '%s' "
> >                 "does not support live migration",
> >                 bdrv_get_device_or_node_name(bs));
> > -    migrate_add_blocker(s->migration_blocker);
> > +    ret = migrate_add_blocker(s->migration_blocker, errp);
> > +    if (ret < 0) {
> > +        error_free(s->migration_blocker);
> > +        goto fail;
> > +    }
> >  
> >      qemu_co_mutex_init(&s->lock);
> >      return 0;
> > diff --git a/block/vdi.c b/block/vdi.c
> > index 96b78d5..2b56f52 100644
> > --- a/block/vdi.c
> > +++ b/block/vdi.c
> > @@ -471,7 +471,11 @@ static int vdi_open(BlockDriverState *bs, QDict 
> > *options, int flags,
> >      error_setg(&s->migration_blocker, "The vdi format used by node '%s' "
> >                 "does not support live migration",
> >                 bdrv_get_device_or_node_name(bs));
> > -    migrate_add_blocker(s->migration_blocker);
> > +    ret = migrate_add_blocker(s->migration_blocker, errp);
> > +    if (ret < 0) {
> > +        error_free(s->migration_blocker);
> > +        goto fail_free_bmap;
> > +    }
> >  
> >      qemu_co_mutex_init(&s->write_lock);
> >  
> > diff --git a/block/vhdx.c b/block/vhdx.c
> > index 0ba2f0a..d81941b 100644
> > --- a/block/vhdx.c
> > +++ b/block/vhdx.c
> > @@ -991,20 +991,24 @@ static int vhdx_open(BlockDriverState *bs, QDict 
> > *options, int flags,
> >          }
> >      }
> >  
> > -    if (flags & BDRV_O_RDWR) {
> > -        ret = vhdx_update_headers(bs, s, false, NULL);
> > -        if (ret < 0) {
> > -            goto fail;
> > -        }
> > -    }
> > -
> > -    /* TODO: differencing files */
> > -
> >      /* Disable migration when VHDX images are used */
> >      error_setg(&s->migration_blocker, "The vhdx format used by node '%s' "
> >                 "does not support live migration",
> >                 bdrv_get_device_or_node_name(bs));
> > -    migrate_add_blocker(s->migration_blocker);
> > +    ret = migrate_add_blocker(s->migration_blocker, errp);
> > +    if (ret < 0) {
> > +        error_free(s->migration_blocker);
> > +        goto fail;
> > +    }
> > +
> > +    if (flags & BDRV_O_RDWR) {
> > +        ret = vhdx_update_headers(bs, s, false, NULL);
> > +        if (ret < 0) {
> > +            goto fail;
> > +        }
> > +    }
> > +
> > +    /* TODO: differencing files */
> >  
> >      return 0;
> >  fail:
> > diff --git a/block/vmdk.c b/block/vmdk.c
> > index a11c27a..4a45a83 100644
> > --- a/block/vmdk.c
> > +++ b/block/vmdk.c
> > @@ -976,7 +976,12 @@ static int vmdk_open(BlockDriverState *bs, QDict 
> > *options, int flags,
> >      error_setg(&s->migration_blocker, "The vmdk format used by node '%s' "
> >                 "does not support live migration",
> >                 bdrv_get_device_or_node_name(bs));
> > -    migrate_add_blocker(s->migration_blocker);
> > +    ret = migrate_add_blocker(s->migration_blocker, errp);
> > +    if (ret < 0) {
> > +        error_free(s->migration_blocker);
> > +        goto fail;
> > +    }
> > +
> >      g_free(buf);
> >      return 0;
> >  
> > diff --git a/block/vpc.c b/block/vpc.c
> > index 8d5886f..299a8c8 100644
> > --- a/block/vpc.c
> > +++ b/block/vpc.c
> > @@ -422,13 +422,17 @@ static int vpc_open(BlockDriverState *bs, QDict 
> > *options, int flags,
> >  #endif
> >      }
> >  
> > -    qemu_co_mutex_init(&s->lock);
> > -
> >      /* Disable migration when VHD images are used */
> >      error_setg(&s->migration_blocker, "The vpc format used by node '%s' "
> >                 "does not support live migration",
> >                 bdrv_get_device_or_node_name(bs));
> > -    migrate_add_blocker(s->migration_blocker);
> > +    ret = migrate_add_blocker(s->migration_blocker, errp);
> > +    if (ret < 0) {
> > +        error_free(s->migration_blocker);
> > +        goto fail;
> > +    }
> > +
> > +    qemu_co_mutex_init(&s->lock);
> >  
> >      return 0;
> >  
> > diff --git a/block/vvfat.c b/block/vvfat.c
> > index ded2109..3de3320 100644
> > --- a/block/vvfat.c
> > +++ b/block/vvfat.c
> > @@ -1185,22 +1185,26 @@ static int vvfat_open(BlockDriverState *bs, QDict 
> > *options, int flags,
> >  
> >      s->sector_count = s->faked_sectors + 
> > s->sectors_per_cluster*s->cluster_count;
> >  
> > -    if (s->first_sectors_number == 0x40) {
> > -        init_mbr(s, cyls, heads, secs);
> > -    }
> > -
> > -    //    assert(is_consistent(s));
> > -    qemu_co_mutex_init(&s->lock);
> > -
> >      /* Disable migration when vvfat is used rw */
> >      if (s->qcow) {
> >          error_setg(&s->migration_blocker,
> >                     "The vvfat (rw) format used by node '%s' "
> >                     "does not support live migration",
> >                     bdrv_get_device_or_node_name(bs));
> > -        migrate_add_blocker(s->migration_blocker);
> > +        ret = migrate_add_blocker(s->migration_blocker, errp);
> > +        if (ret < 0) {
> > +            error_free(s->migration_blocker);
> > +            goto fail;
> > +        }
> >      }
> >  
> > +    if (s->first_sectors_number == 0x40) {
> > +        init_mbr(s, cyls, heads, secs);
> > +    }
> > +
> > +    //    assert(is_consistent(s));
> > +    qemu_co_mutex_init(&s->lock);
> > +
> >      ret = 0;
> >  fail:
> >      qemu_opts_del(opts);
> > diff --git a/hw/9pfs/9p.c b/hw/9pfs/9p.c
> > index faebd91..e72ef43 100644
> > --- a/hw/9pfs/9p.c
> > +++ b/hw/9pfs/9p.c
> > @@ -1013,20 +1013,28 @@ static void coroutine_fn v9fs_attach(void *opaque)
> >          goto out;
> >      }
> >      err += offset;
> > -    memcpy(&s->root_qid, &qid, sizeof(qid));
> > -    trace_v9fs_attach_return(pdu->tag, pdu->id,
> > -                             qid.type, qid.version, qid.path);
> > +
> >      /*
> >       * disable migration if we haven't done already.
> >       * attach could get called multiple times for the same export.
> >       */
> >      if (!s->migration_blocker) {
> > +        int ret;
> >          s->root_fid = fid;
> >          error_setg(&s->migration_blocker,
> >                     "Migration is disabled when VirtFS export path '%s' is 
> > mounted in the guest using mount_tag '%s'",
> >                     s->ctx.fs_root ? s->ctx.fs_root : "NULL", s->tag);
> > -        migrate_add_blocker(s->migration_blocker);
> > +        ret = migrate_add_blocker(s->migration_blocker, NULL);
> > +        if (ret < 0) {
> > +            err = ret;
> > +            clunk_fid(s, fid);
> > +            goto out;
> 
> So this would cause mount(2) in the guest to fail with EBUSY if
> migration is in progress, right ? I guess well configured guests
> should be able to cope with temporary failures when mounting
> a network filesystem and retry later.
> 
> I don't object but I'd like to have some more background... if
> you could point me to the on-list discussion you're mentioning
> in the cover letter, that'd be great. :)

See the discussion on:
https://lists.nongnu.org/archive/html/qemu-devel/2016-12/msg01185.html

note, it might be best to special case 9pfs here; it's unusual
in that it's unusable in that it always does the migration blocker
when in use; everywhere else has the flag in the VMStateDescription
or only blocks in specific cases.

Dave

> Thanks.
> 
> --
> Greg
> 
> > +        }
> >      }
> > +
> > +    memcpy(&s->root_qid, &qid, sizeof(qid));
> > +    trace_v9fs_attach_return(pdu->tag, pdu->id,
> > +                             qid.type, qid.version, qid.path);
> >  out:
> >      put_fid(pdu, fidp);
> >  out_nofid:
> > diff --git a/hw/display/virtio-gpu.c b/hw/display/virtio-gpu.c
> > index 5f32e1a..6e60b8c 100644
> > --- a/hw/display/virtio-gpu.c
> > +++ b/hw/display/virtio-gpu.c
> > @@ -1108,14 +1108,6 @@ static void virtio_gpu_device_realize(DeviceState 
> > *qdev, Error **errp)
> >          return;
> >      }
> >  
> > -    g->config_size = sizeof(struct virtio_gpu_config);
> > -    g->virtio_config.num_scanouts = g->conf.max_outputs;
> > -    virtio_init(VIRTIO_DEVICE(g), "virtio-gpu", VIRTIO_ID_GPU,
> > -                g->config_size);
> > -
> > -    g->req_state[0].width = 1024;
> > -    g->req_state[0].height = 768;
> > -
> >      g->use_virgl_renderer = false;
> >  #if !defined(CONFIG_VIRGL) || defined(HOST_WORDS_BIGENDIAN)
> >      have_virgl = false;
> > @@ -1127,6 +1119,22 @@ static void virtio_gpu_device_realize(DeviceState 
> > *qdev, Error **errp)
> >      }
> >  
> >      if (virtio_gpu_virgl_enabled(g->conf)) {
> > +        error_setg(&g->migration_blocker, "virgl is not yet migratable");
> > +        if (migrate_add_blocker(g->migration_blocker, errp) < 0) {
> > +            error_free(g->migration_blocker);
> > +            return;
> > +        }
> > +    }
> > +
> > +    g->config_size = sizeof(struct virtio_gpu_config);
> > +    g->virtio_config.num_scanouts = g->conf.max_outputs;
> > +    virtio_init(VIRTIO_DEVICE(g), "virtio-gpu", VIRTIO_ID_GPU,
> > +                g->config_size);
> > +
> > +    g->req_state[0].width = 1024;
> > +    g->req_state[0].height = 768;
> > +
> > +    if (virtio_gpu_virgl_enabled(g->conf)) {
> >          /* use larger control queue in 3d mode */
> >          g->ctrl_vq   = virtio_add_queue(vdev, 256, 
> > virtio_gpu_handle_ctrl_cb);
> >          g->cursor_vq = virtio_add_queue(vdev, 16, 
> > virtio_gpu_handle_cursor_cb);
> > @@ -1152,11 +1160,6 @@ static void virtio_gpu_device_realize(DeviceState 
> > *qdev, Error **errp)
> >              dpy_gfx_replace_surface(g->scanout[i].con, NULL);
> >          }
> >      }
> > -
> > -    if (virtio_gpu_virgl_enabled(g->conf)) {
> > -        error_setg(&g->migration_blocker, "virgl is not yet migratable");
> > -        migrate_add_blocker(g->migration_blocker);
> > -    }
> >  }
> >  
> >  static void virtio_gpu_device_unrealize(DeviceState *qdev, Error **errp)
> > diff --git a/hw/misc/ivshmem.c b/hw/misc/ivshmem.c
> > index abeaf3d..585cc5b 100644
> > --- a/hw/misc/ivshmem.c
> > +++ b/hw/misc/ivshmem.c
> > @@ -903,9 +903,6 @@ static void ivshmem_common_realize(PCIDevice *dev, 
> > Error **errp)
> >          }
> >      }
> >  
> > -    vmstate_register_ram(s->ivshmem_bar2, DEVICE(s));
> > -    pci_register_bar(PCI_DEVICE(s), 2, attr, s->ivshmem_bar2);
> > -
> >      if (s->master == ON_OFF_AUTO_AUTO) {
> >          s->master = s->vm_id == 0 ? ON_OFF_AUTO_ON : ON_OFF_AUTO_OFF;
> >      }
> > @@ -913,8 +910,14 @@ static void ivshmem_common_realize(PCIDevice *dev, 
> > Error **errp)
> >      if (!ivshmem_is_master(s)) {
> >          error_setg(&s->migration_blocker,
> >                     "Migration is disabled when using feature 'peer mode' 
> > in device 'ivshmem'");
> > -        migrate_add_blocker(s->migration_blocker);
> > +        if (migrate_add_blocker(s->migration_blocker, errp) < 0) {
> > +            error_free(s->migration_blocker);
> > +            return;
> > +        }
> >      }
> > +
> > +    vmstate_register_ram(s->ivshmem_bar2, DEVICE(s));
> > +    pci_register_bar(PCI_DEVICE(s), 2, attr, s->ivshmem_bar2);
> >  }
> >  
> >  static void ivshmem_exit(PCIDevice *dev)
> > diff --git a/hw/scsi/vhost-scsi.c b/hw/scsi/vhost-scsi.c
> > index 5b26946..ff503d0 100644
> > --- a/hw/scsi/vhost-scsi.c
> > +++ b/hw/scsi/vhost-scsi.c
> > @@ -238,8 +238,14 @@ static void vhost_scsi_realize(DeviceState *dev, Error 
> > **errp)
> >                                 vhost_dummy_handle_output);
> >      if (err != NULL) {
> >          error_propagate(errp, err);
> > -        close(vhostfd);
> > -        return;
> > +        goto close_fd;
> > +    }
> > +
> > +    error_setg(&s->migration_blocker,
> > +               "vhost-scsi does not support migration");
> > +    ret = migrate_add_blocker(s->migration_blocker, errp);
> > +    if (ret < 0) {
> > +        goto free_blocker;
> >      }
> >  
> >      s->dev.nvqs = VHOST_SCSI_VQ_NUM_FIXED + vs->conf.num_queues;
> > @@ -252,7 +258,7 @@ static void vhost_scsi_realize(DeviceState *dev, Error 
> > **errp)
> >      if (ret < 0) {
> >          error_setg(errp, "vhost-scsi: vhost initialization failed: %s",
> >                     strerror(-ret));
> > -        return;
> > +        goto free_vqs;
> >      }
> >  
> >      /* At present, channel and lun both are 0 for bootable vhost-scsi disk 
> > */
> > @@ -261,9 +267,16 @@ static void vhost_scsi_realize(DeviceState *dev, Error 
> > **errp)
> >      /* Note: we can also get the minimum tpgt from kernel */
> >      s->target = vs->conf.boot_tpgt;
> >  
> > -    error_setg(&s->migration_blocker,
> > -            "vhost-scsi does not support migration");
> > -    migrate_add_blocker(s->migration_blocker);
> > +    return;
> > +
> > + free_vqs:
> > +    migrate_del_blocker(s->migration_blocker);
> > +    g_free(s->dev.vqs);
> > + free_blocker:
> > +    error_free(s->migration_blocker);
> > + close_fd:
> > +    close(vhostfd);
> > +    return;
> >  }
> >  
> >  static void vhost_scsi_unrealize(DeviceState *dev, Error **errp)
> > diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
> > index f7f7023..416fada 100644
> > --- a/hw/virtio/vhost.c
> > +++ b/hw/virtio/vhost.c
> > @@ -1157,7 +1157,13 @@ int vhost_dev_init(struct vhost_dev *hdev, void 
> > *opaque,
> >      }
> >  
> >      if (hdev->migration_blocker != NULL) {
> > -        migrate_add_blocker(hdev->migration_blocker);
> > +        Error *local_err;
> > +        r = migrate_add_blocker(hdev->migration_blocker, &local_err);
> > +        if (r < 0) {
> > +            error_report_err(local_err);
> > +            error_free(hdev->migration_blocker);
> > +            goto fail_busyloop;
> > +        }
> >      }
> >  
> >      hdev->mem = g_malloc0(offsetof(struct vhost_memory, regions));
> > diff --git a/include/migration/migration.h b/include/migration/migration.h
> > index c309d23..8a91215 100644
> > --- a/include/migration/migration.h
> > +++ b/include/migration/migration.h
> > @@ -240,6 +240,7 @@ void remove_migration_state_change_notifier(Notifier 
> > *notify);
> >  MigrationState *migrate_init(const MigrationParams *params);
> >  bool migration_is_blocked(Error **errp);
> >  bool migration_in_setup(MigrationState *);
> > +bool migration_is_idle(MigrationState *s);
> >  bool migration_has_finished(MigrationState *);
> >  bool migration_has_failed(MigrationState *);
> >  /* True if outgoing migration has entered postcopy phase */
> > @@ -284,8 +285,11 @@ int ram_postcopy_incoming_init(MigrationIncomingState 
> > *mis);
> >   * @migrate_add_blocker - prevent migration from proceeding
> >   *
> >   * @reason - an error to be returned whenever migration is attempted
> > + * @errp - [out] The reason (if any) we cannot block migration right now.
> > + *
> > + * @returns - 0 on success, -EBUSY on failure, with errp set.
> >   */
> > -void migrate_add_blocker(Error *reason);
> > +int migrate_add_blocker(Error *reason, Error **errp);
> >  
> >  /**
> >   * @migrate_del_blocker - remove a blocking error from migration
> > diff --git a/migration/migration.c b/migration/migration.c
> > index f498ab8..713e012 100644
> > --- a/migration/migration.c
> > +++ b/migration/migration.c
> > @@ -1044,6 +1044,31 @@ bool 
> > migration_in_postcopy_after_devices(MigrationState *s)
> >      return migration_in_postcopy(s) && s->postcopy_after_devices;
> >  }
> >  
> > +bool migration_is_idle(MigrationState *s)
> > +{
> > +    if (!s) {
> > +        s = migrate_get_current();
> > +    }
> > +
> > +    switch (s->state) {
> > +    case MIGRATION_STATUS_NONE:
> > +    case MIGRATION_STATUS_CANCELLED:
> > +    case MIGRATION_STATUS_COMPLETED:
> > +    case MIGRATION_STATUS_FAILED:
> > +        return true;
> > +    case MIGRATION_STATUS_SETUP:
> > +    case MIGRATION_STATUS_CANCELLING:
> > +    case MIGRATION_STATUS_ACTIVE:
> > +    case MIGRATION_STATUS_POSTCOPY_ACTIVE:
> > +    case MIGRATION_STATUS_COLO:
> > +        return false;
> > +    case MIGRATION_STATUS__MAX:
> > +        g_assert_not_reached();
> > +    }
> > +
> > +    return false;
> > +}
> > +
> >  MigrationState *migrate_init(const MigrationParams *params)
> >  {
> >      MigrationState *s = migrate_get_current();
> > @@ -1086,9 +1111,15 @@ MigrationState *migrate_init(const MigrationParams 
> > *params)
> >  
> >  static GSList *migration_blockers;
> >  
> > -void migrate_add_blocker(Error *reason)
> > +int migrate_add_blocker(Error *reason, Error **errp)
> >  {
> > -    migration_blockers = g_slist_prepend(migration_blockers, reason);
> > +    if (migration_is_idle(NULL)) {
> > +        migration_blockers = g_slist_prepend(migration_blockers, reason);
> > +        return 0;
> > +    }
> > +
> > +    error_setg(errp, "Cannot block a migration already in-progress");
> > +    return -EBUSY;
> >  }
> >  
> >  void migrate_del_blocker(Error *reason)
> > diff --git a/stubs/migr-blocker.c b/stubs/migr-blocker.c
> > index 8ab3604..a5ba18f 100644
> > --- a/stubs/migr-blocker.c
> > +++ b/stubs/migr-blocker.c
> > @@ -2,8 +2,9 @@
> >  #include "qemu-common.h"
> >  #include "migration/migration.h"
> >  
> > -void migrate_add_blocker(Error *reason)
> > +int migrate_add_blocker(Error *reason, Error **errp)
> >  {
> > +    return 0;
> >  }
> >  
> >  void migrate_del_blocker(Error *reason)
> > diff --git a/target-i386/kvm.c b/target-i386/kvm.c
> > index f62264a..8abb54d 100644
> > --- a/target-i386/kvm.c
> > +++ b/target-i386/kvm.c
> > @@ -961,7 +961,11 @@ int kvm_arch_init_vcpu(CPUState *cs)
> >          error_setg(&invtsc_mig_blocker,
> >                     "State blocked by non-migratable CPU device"
> >                     " (invtsc flag)");
> > -        migrate_add_blocker(invtsc_mig_blocker);
> > +        r = migrate_add_blocker(invtsc_mig_blocker, NULL);
> > +        if (r < 0) {
> > +            fprintf(stderr, "migrate_add_blocker failed\n");
> > +            goto efail;
> > +        }
> >          /* for savevm */
> >          vmstate_x86_cpu.unmigratable = 1;
> >      }
> > @@ -969,12 +973,12 @@ int kvm_arch_init_vcpu(CPUState *cs)
> >      cpuid_data.cpuid.padding = 0;
> >      r = kvm_vcpu_ioctl(cs, KVM_SET_CPUID2, &cpuid_data);
> >      if (r) {
> > -        return r;
> > +        goto fail;
> >      }
> >  
> >      r = kvm_arch_set_tsc_khz(cs);
> >      if (r < 0) {
> > -        return r;
> > +        goto fail;
> >      }
> >  
> >      /* vcpu's TSC frequency is either specified by user, or following
> > @@ -1001,6 +1005,12 @@ int kvm_arch_init_vcpu(CPUState *cs)
> >      }
> >  
> >      return 0;
> > +
> > + fail:
> > +    migrate_del_blocker(invtsc_mig_blocker);
> > + efail:
> > +    error_free(invtsc_mig_blocker);
> > +    return r;
> >  }
> >  
> >  void kvm_arch_reset_vcpu(X86CPU *cpu)
> 
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK