Synchronize plugin switching

1 files changed, 15 insertions, 7 deletions

diff --git a/litmus/litmus.c b/litmus/litmus.c
index 70a7f628455b..e43596a5104c 100644
--- a/litmus/litmus.c
+++ b/litmus/litmus.c
@@ -24,6 +24,8 @@
 /* Number of RT tasks that exist in the system */
 atomic_t rt_task_count          = ATOMIC_INIT(0);
 static DEFINE_SPINLOCK(task_transition_lock);
+/* synchronize plugin switching */
+atomic_t cannot_use_plugin      = ATOMIC_INIT(0);
 
 /* Give log messages sequential IDs. */
 atomic_t __log_seq_no = ATOMIC_INIT(0);
@@ -369,17 +371,17 @@ void litmus_exit_task(struct task_struct* tsk)
         }
 }
 
+/* IPI callback to synchronize plugin switching */
+static void synch_on_plugin_switch(void* info)
+{
+        while (atomic_read(&cannot_use_plugin))
+                cpu_relax();
+}
+
 /* Switching a plugin in use is tricky.
  * We must watch out that no real-time tasks exists
  * (and that none is created in parallel) and that the plugin is not
  * currently in use on any processor (in theory).
- *
- * FIXME we don't enforce the second part since it is unlikely to cause
- * any trouble by itself as long as we don't unload modules.
- * - This is causing problems with C-EDF when reloading clusters configuration
- *   on big SMP machines (e.g., 24 cores). The plugin is in use on some
- *   processor when we unload is, and this cause troubles as 
- *   we free the clusters while these are used :(
  */
 int switch_sched_plugin(struct sched_plugin* plugin)
 {
@@ -388,6 +390,11 @@ int switch_sched_plugin(struct sched_plugin* plugin)
 
         BUG_ON(!plugin);
 
+        /* forbid other cpus to use the plugin */
+        atomic_set(&cannot_use_plugin, 1);
+        /* send IPI to force other CPUs to synch with us */
+        smp_call_function(synch_on_plugin_switch, NULL, 0);
+
         /* stop task transitions */
         spin_lock_irqsave(&task_transition_lock, flags);
 
@@ -408,6 +415,7 @@ int switch_sched_plugin(struct sched_plugin* plugin)
                 ret = -EBUSY;
 out:
         spin_unlock_irqrestore(&task_transition_lock, flags);
+        atomic_set(&cannot_use_plugin, 0);
         return ret;
 }