[PATCH] task_lock commentary fixes

From: Manfred Spraul <manfred@colorfullife.com>

Update and clarify the incorrect commentary around task_lock()

include/linux/sched.h

@@ -686,7 +686,11 @@ static inline int thread_group_empty(task_t *p)
 
 extern void unhash_process(struct task_struct *p);
 
-/* Protects ->fs, ->files, ->mm, and synchronises with wait4().  Nests inside tasklist_lock */
+/* Protects ->fs, ->files, ->mm, and synchronises with wait4().
+ * Nests both inside and outside of read_lock(&tasklist_lock).
+ * It must not be nested with write_lock_irq(&tasklist_lock),
+ * neither inside nor outside.
+ */
 static inline void task_lock(struct task_struct *p)
 {
 	spin_lock(&p->alloc_lock);