[Xen-devel] [PATCH] [Mini-OS] Fix domain blocking race

[Samuel Thibault <samuel.thibault@xxxxxxxxxxxxx>]

A callback which wakes a thread may happen between the moment schedule()
gives hand to the idle thread and the latter blocks the domain.  Idle
hence needs to atomically check that no thread is running and block,
else awoken threads may have to wait up to 10 seconds.

Signed-off-by: Samuel Thibault <samuel.thibault@xxxxxxxxxx>

diff -r dc9246357cdb extras/mini-os/sched.c
--- a/extras/mini-os/sched.c    Fri Nov 23 16:42:44 2007 +0000
+++ b/extras/mini-os/sched.c    Fri Nov 23 18:11:18 2007 +0000
@@ -216,12 +216,29 @@
 void idle_thread_fn(void *unused)
 {
     s_time_t until;
+    unsigned long flags;
+    struct list_head *iterator;
+    struct thread *next, *thread;
     for(;;)
     {
         schedule();
-        /* block until the next timeout expires, or for 10 secs, whichever 
comes first */
-        until = blocking_time();
-        block_domain(until);
+        next = NULL;
+        local_irq_save(flags);
+        list_for_each(iterator, &idle_thread->thread_list)
+        {
+            thread = list_entry(iterator, struct thread, thread_list);
+            if(is_runnable(thread)) 
+            {
+                next = thread;
+                break;
+            }
+        }
+        if (!next) {
+            /* block until the next timeout expires, or for 10 secs, whichever 
comes first */
+            until = blocking_time();
+            block_domain(until);
+        }
+        local_irq_restore(flags);
         wake_expired();
     }
 }

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