virthread: Free thread name only after worker has finished

When spawning a thread via our virThread APIs we let pthread
spawn this helper thread which sets couple of thread local
variables (e.g. thread job name or thread worker name) and as of
v6.1.0-40-gc85256b3 it also sets pthread name (which is then
visible in `ps' output for instance). Only after these steps the
intended function is called. However, just before calling it we
free the buffer that holds the thread name which results in
invalid memory reads:

==47027== Invalid read of size 1
==47027==    at 0x48389C2: strlen (vg_replace_strmem.c:459)
==47027==    by 0x58BB3D6: __vfprintf_internal (vfprintf-internal.c:1645)
==47027==    by 0x58CE6E0: __vasprintf_internal (vasprintf.c:57)
==47027==    by 0x574BA28: g_vasprintf (in /usr/lib64/libglib-2.0.so.0.6000.7)
==47027==    by 0x57240CC: g_strdup_vprintf (in /usr/lib64/libglib-2.0.so.0.6000.7)
==47027==    by 0x48E0EFA: vir_g_strdup_vprintf (glibcompat.c:209)
==47027==    by 0x493AA05: virLogVMessage (virlog.c:573)
==47027==    by 0x493A8FE: virLogMessage (virlog.c:513)
==47027==    by 0x4992FC7: virThreadJobClear (virthreadjob.c:121)
==47027==    by 0x4992844: virThreadHelper (virthread.c:237)
==47027==    by 0x5817496: start_thread (pthread_create.c:486)
==47027==    by 0x59563CE: clone (clone.S:95)

The problem is that neither virThreadJobSetWorker() nor
virThreadJobSet() create a copy of passed name. They just set a
thread local variable to point to the buffer which is then
freed. Moving the free towards the end of the wrapper function
solves the issue.
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>
Reviewed-by: NDaniel P. Berrangé <berrange@redhat.com>

src/util/virthread.c

@@ -217,7 +217,6 @@ static void *virThreadHelper(void *data)
     } else {
         thname = g_strdup(local.name);
     }
-    g_free(local.name);
 
 #if defined(__linux__) || defined(WIN32)
     pthread_setname_np(pthread_self(), thname);
@@ -236,6 +235,7 @@ static void *virThreadHelper(void *data)
     if (!local.worker)
         virThreadJobClear(0);
 
+    g_free(local.name);
     return NULL;
 }