[Qemu-devel] [for-2.7 PATCH v3 11/15] spapr_drc: Prevent detach racing against attach for CPU DR

[Bharata B Rao <bharata@linux.vnet.ibm.com>]

If a CPU is hot removed while hotplug of the same is still in progress,
the guest crashes. Prevent this by ensuring that detach is done only
after attach has completed.

The existing code already prevents such race for PCI hotplug. However
given that CPU is a logical DR unlike PCI and starts with ISOLATED
state, we need a logic that works for CPU too.

Signed-off-by: Bharata B Rao <bharata@linux.vnet.ibm.com>
Reviewed-by: Michael Roth <mdroth@linux.vnet.ibm.com>
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
               [Don't set awaiting_attach for PCI devices]
---
 hw/ppc/spapr_drc.c         | 12 ++++++++++++
 include/hw/ppc/spapr_drc.h |  1 +
 2 files changed, 13 insertions(+)

diff --git a/hw/ppc/spapr_drc.c b/hw/ppc/spapr_drc.c
index 1f5f1d7..e146267 100644
--- a/hw/ppc/spapr_drc.c
+++ b/hw/ppc/spapr_drc.c
@@ -140,6 +140,8 @@ static uint32_t set_allocation_state(sPAPRDRConnector *drc,
             DPRINTFN("finalizing device removal");
             drck->detach(drc, DEVICE(drc->dev), drc->detach_cb,
                          drc->detach_cb_opaque, NULL);
+        } else if (drc->allocation_state == SPAPR_DR_ALLOCATION_STATE_USABLE) {
+            drc->awaiting_allocation = false;
         }
     }
     return RTAS_OUT_SUCCESS;
@@ -376,6 +378,10 @@ static void attach(sPAPRDRConnector *drc, DeviceState *d, void *fdt,
     drc->signalled = (drc->type != SPAPR_DR_CONNECTOR_TYPE_PCI)
                      ? true : coldplug;
 
+    if (drc->type != SPAPR_DR_CONNECTOR_TYPE_PCI) {
+        drc->awaiting_allocation = true;
+    }
+
     object_property_add_link(OBJECT(drc), "device",
                              object_get_typename(OBJECT(drc->dev)),
                              (Object **)(&drc->dev),
@@ -424,6 +430,12 @@ static void detach(sPAPRDRConnector *drc, DeviceState *d,
         return;
     }
 
+    if (drc->awaiting_allocation) {
+        drc->awaiting_release = true;
+        DPRINTFN("awaiting allocation to complete before removal");
+        return;
+    }
+
     drc->indicator_state = SPAPR_DR_INDICATOR_STATE_INACTIVE;
 
     if (drc->detach_cb) {
diff --git a/include/hw/ppc/spapr_drc.h b/include/hw/ppc/spapr_drc.h
index fa21ba0..08e8411 100644
--- a/include/hw/ppc/spapr_drc.h
+++ b/include/hw/ppc/spapr_drc.h
@@ -152,6 +152,7 @@ typedef struct sPAPRDRConnector {
 
     bool awaiting_release;
     bool signalled;
+    bool awaiting_allocation;
 
     /* device pointer, via link property */
     DeviceState *dev;
-- 
2.1.0