[PATCH for-5.0 1/2] hostmem: set default prealloc_threads to valid value

[Igor Mammedov]

Commit 4ebc74dbbf removed default prealloc_threads initialization
by mistake, and that makes QEMU crash with division on zero at
  numpages_per_thread = numpages / memset_num_threads;
when QEMU is started with following backend
  -object memory-backend-ram,id=ram-node0,prealloc=yes,size=128M

Return back initialization removed by 4ebc74dbbf to fix issue.

Fixes: 4ebc74dbbf7ad50e4101629f3f5da5fdc1544051
Reported-by: Raphael Norwitz <address@hidden>
Signed-off-by: Igor Mammedov <address@hidden>
---
 backends/hostmem.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/backends/hostmem.c b/backends/hostmem.c
index a70867b255..327f9eebc3 100644
--- a/backends/hostmem.c
+++ b/backends/hostmem.c
@@ -280,6 +280,7 @@ static void host_memory_backend_init(Object *obj)
     /* TODO: convert access to globals to compat properties */
     backend->merge = machine_mem_merge(machine);
     backend->dump = machine_dump_guest_core(machine);
+    backend->prealloc_threads = 1;
 }
 
 static void host_memory_backend_post_init(Object *obj)
-- 
2.18.1