[PATCH] machdev, pci-arbiter, rumpdisk: Fix race condition in bootstrap

[Damien Zammit]

This fixes a known race condition in bootstrapping by
separating the fsys_startup call from the server demuxer loop
into two separate functions that the caller can decide
when to call.
---
 libmachdev/machdev.h       |  3 ++-
 libmachdev/trivfs_server.c | 18 ++++++++++++------
 pci-arbiter/main.c         | 31 ++++++++++++-------------------
 rumpdisk/main.c            |  4 +++-
 4 files changed, 29 insertions(+), 27 deletions(-)

diff --git a/libmachdev/machdev.h b/libmachdev/machdev.h
index e1833cff..05d0c330 100644
--- a/libmachdev/machdev.h
+++ b/libmachdev/machdev.h
@@ -37,7 +37,8 @@ void * machdev_server(void *);
 error_t machdev_create_device_port (size_t size, void *result);
 int machdev_trivfs_init(int argc, char **argv, mach_port_t 
bootstrap_resume_task, const char *name, const char *path, mach_port_t 
*bootstrap);
 int machdev_demuxer(mach_msg_header_t *inp, mach_msg_header_t *outp);
-void machdev_trivfs_server(mach_port_t bootstrap);
+void machdev_trivfs_server_startup(mach_port_t bootstrap);
+void * do_machdev_trivfs_server(void *);
 boolean_t machdev_is_master_device (mach_port_t port);

 #endif
diff --git a/libmachdev/trivfs_server.c b/libmachdev/trivfs_server.c
index 21684dab..79bbcacc 100644
--- a/libmachdev/trivfs_server.c
+++ b/libmachdev/trivfs_server.c
@@ -84,6 +84,9 @@ static task_t parent_task;
 /* Our argument vector */
 static char **machdev_argv;

+/* Our trivfs control port to use in server loop */
+static struct trivfs_control *global_fsys;
+
 static void
 install_as_translator (mach_port_t bootport)
 {
@@ -513,9 +516,8 @@ trivfs_modify_stat (struct trivfs_protid *cred, 
io_statbuf_t *stat)
 }

 void
-machdev_trivfs_server(mach_port_t bootstrap)
+machdev_trivfs_server_startup(mach_port_t bootstrap)
 {
-  struct trivfs_control *fsys = NULL;
   int err;

   if (bootstrapping == FALSE)
@@ -523,7 +525,7 @@ machdev_trivfs_server(mach_port_t bootstrap)
       /* This path is executed when a parent exists */
       err = trivfs_startup (bootstrap, 0,
                             trivfs_cntl_class, port_bucket,
-                            trivfs_protid_class, port_bucket, &fsys);
+                            trivfs_protid_class, port_bucket, &global_fsys);
       mach_port_deallocate (mach_task_self (), bootstrap);
       if (err)
         error (1, err, "Contacting parent");
@@ -532,14 +534,18 @@ machdev_trivfs_server(mach_port_t bootstrap)
     }
   else
     {
-      fsys = control;
+      global_fsys = control;
     }
+}

+void *
+do_machdev_trivfs_server(void *arg)
+{
   /* Launch.  */
   do
     {
       ports_manage_port_operations_one_thread (port_bucket, demuxer, 0);
-    } while (trivfs_goaway (fsys, 0));
+    } while (trivfs_goaway (global_fsys, 0));

-  /* Never reached */
+  return NULL;
 }
diff --git a/pci-arbiter/main.c b/pci-arbiter/main.c
index ec9be796..00180b24 100644
--- a/pci-arbiter/main.c
+++ b/pci-arbiter/main.c
@@ -188,7 +188,7 @@ main (int argc, char **argv)
   error_t err;
   mach_port_t bootstrap;
   mach_port_t next_task;
-  pthread_t t, nt;
+  pthread_t t, mt;
   file_t underlying_node = MACH_PORT_NULL;

   /* Parse options */
@@ -214,7 +214,7 @@ main (int argc, char **argv)
       machdev_device_init ();
       err = pthread_create (&t, NULL, machdev_server, NULL);
       if (err)
-        error (1, err, "Creating machdev thread");
+        error (1, err, "Creating machdev_server thread");
       pthread_detach (t);
     }
   else
@@ -238,17 +238,7 @@ main (int argc, char **argv)
     error (1, err, "Starting the PCI system");

   if (next_task != MACH_PORT_NULL)
-    {
-      void *run_server(void *arg) {
-       machdev_trivfs_server(bootstrap);
-       return NULL;
-      }
-
-      pthread_t t;
-      pthread_create(&t, NULL, run_server, NULL);
-      pthread_detach(t);
-      /* Timer started, quickly do all these next, before we call rump_init */
-    }
+    machdev_trivfs_server_startup (bootstrap);

   if (next_task == MACH_PORT_NULL)
     underlying_node = netfs_startup (bootstrap, O_READ);
@@ -275,13 +265,16 @@ main (int argc, char **argv)
   if (err)
     error (1, err, "Setting permissions");

-  err = pthread_create (&nt, NULL, netfs_server_func, NULL);
-  if (err)
-    error (1, err, "Creating netfs loop thread");
-  pthread_detach (nt);
+  if (next_task != MACH_PORT_NULL)
+    {
+      err = pthread_create(&mt, NULL, do_machdev_trivfs_server, NULL);
+      if (err)
+        error(1, err, "Creating do_machdev_trivfs_server thread");
+      pthread_detach(mt);
+    }
+
+  netfs_server_func (NULL);

-  /* Let the other threads do their job */
-  pthread_exit(NULL);
   /* Never reached */
   return 0;
 }
diff --git a/rumpdisk/main.c b/rumpdisk/main.c
index 9a353541..a502ca2b 100644
--- a/rumpdisk/main.c
+++ b/rumpdisk/main.c
@@ -141,6 +141,8 @@ main (int argc, char **argv)
   if (err)
     return err;
   pthread_detach (t);
-  machdev_trivfs_server (bootstrap);
+  machdev_trivfs_server_startup (bootstrap);
+  do_machdev_trivfs_server (NULL);
+  /* Never reached */
   return 0;
 }
--
2.34.1