Attempt to fix race condition with plugin switchingwip-fix-switch-jerickso

1 files changed, 9 insertions, 0 deletions

diff --git a/litmus/litmus.c b/litmus/litmus.c
index 0756d0156f8f..1dbe8e52839f 100644
--- a/litmus/litmus.c
+++ b/litmus/litmus.c
@@ -22,6 +22,7 @@ atomic_t rt_task_count 		= ATOMIC_INIT(0);
 static DEFINE_RAW_SPINLOCK(task_transition_lock);
 /* synchronize plugin switching */
 atomic_t cannot_use_plugin      = ATOMIC_INIT(0);
+atomic_t cpus_waiting_for_plugin = ATOMIC_INIT(0);
 
 /* Give log messages sequential IDs. */
 atomic_t __log_seq_no = ATOMIC_INIT(0);
@@ -382,6 +383,7 @@ void litmus_exit_task(struct task_struct* tsk)
 /* IPI callback to synchronize plugin switching */
 static void synch_on_plugin_switch(void* info)
 {
+        atomic_inc(&cpus_waiting_for_plugin);
         while (atomic_read(&cannot_use_plugin))
                 cpu_relax();
 }
@@ -400,9 +402,16 @@ int switch_sched_plugin(struct sched_plugin* plugin)
 
         /* forbid other cpus to use the plugin */
         atomic_set(&cannot_use_plugin, 1);
+
+        atomic_set(&cpus_waiting_for_plugin, 0);
+
         /* send IPI to force other CPUs to synch with us */
         smp_call_function(synch_on_plugin_switch, NULL, 0);
 
+        /* wait until all other CPUs have started synch */
+        while (atomic_read(&cpus_waiting_for_plugin) < num_online_cpus() - 1)
+                cpu_relax();
+
         /* stop task transitions */
         raw_spin_lock_irqsave(&task_transition_lock, flags);