fix qemu exit on memory hotplug when allocation fails at prealloc time

When adding hostmem backend at runtime, QEMU might exit with error:
  "os_mem_prealloc: Insufficient free host memory pages available to allocate guest RAM"

It happens due to os_mem_prealloc() not handling errors gracefully.

Fix it by passing errp argument so that os_mem_prealloc() could
report error to callers and undo performed allocation when
os_mem_prealloc() fails.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Message-Id: <1469008443-72059-1-git-send-email-imammedo@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 14 insertions, 4 deletions

diff --git a/backends/hostmem.c b/backends/hostmem.c
index ac802570a8..b7a208d0da 100644
--- a/backends/hostmem.c
+++ b/backends/hostmem.c
@@ -203,6 +203,7 @@ static bool host_memory_backend_get_prealloc(Object *obj, Error **errp)
 static void host_memory_backend_set_prealloc(Object *obj, bool value,
                                              Error **errp)
 {
+    Error *local_err = NULL;
     HostMemoryBackend *backend = MEMORY_BACKEND(obj);
 
     if (backend->force_prealloc) {
@@ -223,7 +224,11 @@ static void host_memory_backend_set_prealloc(Object *obj, bool value,
         void *ptr = memory_region_get_ram_ptr(&backend->mr);
         uint64_t sz = memory_region_size(&backend->mr);
 
-        os_mem_prealloc(fd, ptr, sz);
+        os_mem_prealloc(fd, ptr, sz, &local_err);
+        if (local_err) {
+            error_propagate(errp, local_err);
+            return;
+        }
         backend->prealloc = true;
     }
 }
@@ -286,8 +291,7 @@ host_memory_backend_memory_complete(UserCreatable *uc, Error **errp)
     if (bc->alloc) {
         bc->alloc(backend, &local_err);
         if (local_err) {
-            error_propagate(errp, local_err);
-            return;
+            goto out;
         }
 
         ptr = memory_region_get_ram_ptr(&backend->mr);
@@ -343,9 +347,15 @@ host_memory_backend_memory_complete(UserCreatable *uc, Error **errp)
          * specified NUMA policy in place.
          */
         if (backend->prealloc) {
-            os_mem_prealloc(memory_region_get_fd(&backend->mr), ptr, sz);
+            os_mem_prealloc(memory_region_get_fd(&backend->mr), ptr, sz,
+                            &local_err);
+            if (local_err) {
+                goto out;
+            }
         }
     }
+out:
+    error_propagate(errp, local_err);
 }
 
 static bool