Re: [PATCH 2/6] spapr: Fix reset of transient DR connectors

[David Gibson]

On Fri, Dec 18, 2020 at 11:33:56AM +0100, Greg Kurz wrote:
> Documentation of object_property_iter_init() clearly stipulates that
> "it is forbidden to modify the property list while iterating". But this
> is exactly what we do when resetting transient DR connectors during CAS.
> The call to spapr_drc_reset() can finalize the hot-unplug sequence of a
> PHB or a PCI bridge, both of which will then in turn destroy their PCI
> DRCs. This could potentially invalidate the iterator. It is pure luck
> that this haven't caused any issues so far.
> 
> Change spapr_drc_reset() to return true if it caused a device to be
> removed. Restart from scratch in this case. This can potentially
> increase the overall DRC reset time, especially with a high maxmem
> which generates a lot of LMB DRCs. But this kind of setup is rare,
> and so is the use case of rebooting a guest while doing hot-unplug.
> 
> Signed-off-by: Greg Kurz <groug@kaod.org>

Applied, thanks.

> ---
>  include/hw/ppc/spapr_drc.h | 3 ++-
>  hw/ppc/spapr_drc.c         | 6 +++++-
>  hw/ppc/spapr_hcall.c       | 8 +++++++-
>  3 files changed, 14 insertions(+), 3 deletions(-)
> 
> diff --git a/include/hw/ppc/spapr_drc.h b/include/hw/ppc/spapr_drc.h
> index cff5e707d0d9..5d80019f82e2 100644
> --- a/include/hw/ppc/spapr_drc.h
> +++ b/include/hw/ppc/spapr_drc.h
> @@ -224,7 +224,8 @@ static inline bool spapr_drc_hotplugged(DeviceState *dev)
>      return dev->hotplugged && !runstate_check(RUN_STATE_INMIGRATE);
>  }
>  
> -void spapr_drc_reset(SpaprDrc *drc);
> +/* Returns true if an unplug request completed */
> +bool spapr_drc_reset(SpaprDrc *drc);
>  
>  uint32_t spapr_drc_index(SpaprDrc *drc);
>  SpaprDrcType spapr_drc_type(SpaprDrc *drc);
> diff --git a/hw/ppc/spapr_drc.c b/hw/ppc/spapr_drc.c
> index 8d62f55066b6..5b5e2ac58a7e 100644
> --- a/hw/ppc/spapr_drc.c
> +++ b/hw/ppc/spapr_drc.c
> @@ -417,9 +417,10 @@ void spapr_drc_detach(SpaprDrc *drc)
>      spapr_drc_release(drc);
>  }
>  
> -void spapr_drc_reset(SpaprDrc *drc)
> +bool spapr_drc_reset(SpaprDrc *drc)
>  {
>      SpaprDrcClass *drck = SPAPR_DR_CONNECTOR_GET_CLASS(drc);
> +    bool unplug_completed = false;
>  
>      trace_spapr_drc_reset(spapr_drc_index(drc));
>  
> @@ -428,6 +429,7 @@ void spapr_drc_reset(SpaprDrc *drc)
>       */
>      if (drc->unplug_requested) {
>          spapr_drc_release(drc);
> +        unplug_completed = true;
>      }
>  
>      if (drc->dev) {
> @@ -444,6 +446,8 @@ void spapr_drc_reset(SpaprDrc *drc)
>          drc->ccs_offset = -1;
>          drc->ccs_depth = -1;
>      }
> +
> +    return unplug_completed;
>  }
>  
>  static bool spapr_drc_unplug_requested_needed(void *opaque)
> diff --git a/hw/ppc/spapr_hcall.c b/hw/ppc/spapr_hcall.c
> index 4e9d50c254f0..aa22830ac4bd 100644
> --- a/hw/ppc/spapr_hcall.c
> +++ b/hw/ppc/spapr_hcall.c
> @@ -1639,6 +1639,7 @@ static void 
> spapr_handle_transient_dev_before_cas(SpaprMachineState *spapr)
>      ObjectPropertyIterator iter;
>  
>      drc_container = container_get(object_get_root(), "/dr-connector");
> +restart:
>      object_property_iter_init(&iter, drc_container);
>      while ((prop = object_property_iter_next(&iter))) {
>          SpaprDrc *drc;
> @@ -1652,8 +1653,13 @@ static void 
> spapr_handle_transient_dev_before_cas(SpaprMachineState *spapr)
>  
>          /*
>           * This will complete any pending plug/unplug requests.
> +         * In case of a unplugged PHB or PCI bridge, this will
> +         * cause some DRCs to be destroyed and thus potentially
> +         * invalidate the iterator.
>           */
> -        spapr_drc_reset(drc);
> +        if (spapr_drc_reset(drc)) {
> +            goto restart;
> +        }
>      }
>  
>      spapr_clear_pending_hotplug_events(spapr);

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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