libsys: add Tomas Hruby's asynsend barrier

This barrier ensures that all fields of an asynchronously sent
message are properly initialized before the message is marked as
valid.

Change-Id: I7b9590c11c4e040c8f992f1dd2581e54201bf214

diff --git a/minix/lib/libsys/asynsend.c b/minix/lib/libsys/asynsend.c
index 3f414712f7a666d00235dcd198f9b6aba917068e..d6c19eecd8b656133fb9ab1c6748bec2d533838d 100644 (file)
--- a/minix/lib/libsys/asynsend.c
+++ b/minix/lib/libsys/asynsend.c
@@ -126,6 +126,7 @@ int fl;
   fl |= AMF_VALID;     /* Mark in use */
   msgtable[next_slot].dst = dst;
   msgtable[next_slot].msg = *mp;
+  __insn_barrier();
   msgtable[next_slot].flags = fl;              /* Has to be last. The kernel 
                                                 * scans this table while we
                                                 * are sleeping.