When os_mem_prealloc() fails, file_ram_alloc() calls qemu_ram_munmap()
and returns null.  Except it doesn't when its @errp argument is null,
because it checks for failure with (errp && *errp).  Introduced in
commit 056b68af77 "fix qemu exit on memory hotplug when allocation
fails at prealloc time".

No caller actually passes null.

Fix anyway: splice in a local Error *err, and error_propagate().

Cc: Igor Mammedov <imammedo@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Message-Id: <20191204093625.14836-6-armbru@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
---
 exec.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/exec.c b/exec.c
index a34c348184..6bd4aa1d87 100644
--- a/exec.c
+++ b/exec.c
@@ -1843,6 +1843,7 @@ static void *file_ram_alloc(RAMBlock *block,
                             bool truncate,
                             Error **errp)
 {
+    Error *err = NULL;
     MachineState *ms = MACHINE(qdev_get_machine());
     void *area;
 
@@ -1900,8 +1901,9 @@ static void *file_ram_alloc(RAMBlock *block,
     }
 
     if (mem_prealloc) {
-        os_mem_prealloc(fd, area, memory, ms->smp.cpus, errp);
-        if (errp && *errp) {
+        os_mem_prealloc(fd, area, memory, ms->smp.cpus, &err);
+        if (err) {
+            error_propagate(errp, err);
             qemu_ram_munmap(fd, area, memory);
             return NULL;
         }
-- 
2.21.0