Changeset 13964ef in mainline

Timestamp:

2008-11-22T17:10:12Z (16 years ago)

Author:

Jiri Svoboda <jirik.svoboda@…>

Branches:

lfn, master, serial, ticket/834-toolchain-update, topic/msim-upgrade, topic/simplify-dev-export

Children:

0aa1665

Parents:

2eb893b

Message:

Fix race that allowed Udebug to report THREAD_B events for threads already reported with THREAD_READ.

Location:

kernel/generic

Files:

• include/udebug/udebug.h (modified) (1 diff)
• src/proc/thread.c (modified) (1 diff)
• src/udebug/udebug.c (modified) (2 diffs)

kernel/generic/include/udebug/udebug.h

@@ -195 +195 @@
     bool end_variant);
 
-void udebug_thread_b_event(struct thread *t);
+void udebug_thread_b_event_attach(struct thread *t, struct task *ta);
 void udebug_thread_e_event(void);
 

kernel/generic/src/proc/thread.c

@@ -764 +764 @@
                          }
                 }
+#ifdef CONFIG_UDEBUG
+                /*
+                 * Generate udebug THREAD_B event and attach the thread.
+                 * This must be done atomically (with the debug locks held),
+                 * otherwise we would either miss some thread or receive
+                 * THREAD_B events for threads that already existed
+                 * and could be detected with THREAD_READ before.
+                 */
+                udebug_thread_b_event_attach(t, TASK);
+#else
                 thread_attach(t, TASK);
+#endif
                 thread_ready(t);
-
-#ifdef CONFIG_UDEBUG
-                /* Generate udebug THREAD_B event */
-                udebug_thread_b_event(t);
-#endif
 
                 return 0;

kernel/generic/src/udebug/udebug.c

@@ -306 +306 @@
 }
 
-/** Thread-creation event hook.
+/** Thread-creation event hook combined with attaching the thread.
  *
  * Must be called when a new userspace thread is created in the debugged
- * task. Generates a THREAD_B event.
+ * task. Generates a THREAD_B event. Also attaches the thread @a t
+ * to the task @a ta.
+ *
+ * This is necessary to avoid a race condition where the BEGIN and THREAD_READ
+ * requests would be handled inbetween attaching the thread and checking it
+ * for being in a debugging session to send the THREAD_B event. We could then
+ * either miss threads or get some threads both in the thread list
+ * and get a THREAD_B event for them.
  *
  * @param t     Structure of the thread being created. Not locked, as the
  *              thread is not executing yet.
- */
-void udebug_thread_b_event(struct thread *t)
+ * @param ta    Task to which the thread should be attached.
+ */
+void udebug_thread_b_event_attach(struct thread *t, struct task *ta)
 {
         call_t *call;
@@ -320 +328 @@
         mutex_lock(&TASK->udebug.lock);
         mutex_lock(&THREAD->udebug.lock);
+
+        thread_attach(t, ta);
 
         LOG("udebug_thread_b_event\n");