Merge branch 'linus' into perf/urgent

[sfrench/cifs-2.6.git] / kernel / ptrace.c

diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index 74a3d693c196810f9eed784a2825ea50a7f9db83..f34d798ef4a25831b98090a7b85fa6d3b93d0de2 100644 (file)
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -324,26 +324,32 @@ int ptrace_detach(struct task_struct *child, unsigned int data)
 }
 
 /*
- * Detach all tasks we were using ptrace on.
+ * Detach all tasks we were using ptrace on. Called with tasklist held
+ * for writing, and returns with it held too. But note it can release
+ * and reacquire the lock.
  */
 void exit_ptrace(struct task_struct *tracer)
 {
        struct task_struct *p, *n;
        LIST_HEAD(ptrace_dead);
 
-       write_lock_irq(&tasklist_lock);
+       if (likely(list_empty(&tracer->ptraced)))
+               return;
+
        list_for_each_entry_safe(p, n, &tracer->ptraced, ptrace_entry) {
                if (__ptrace_detach(tracer, p))
                        list_add(&p->ptrace_entry, &ptrace_dead);
        }
-       write_unlock_irq(&tasklist_lock);
 
+       write_unlock_irq(&tasklist_lock);
        BUG_ON(!list_empty(&tracer->ptraced));
 
        list_for_each_entry_safe(p, n, &ptrace_dead, ptrace_entry) {
                list_del_init(&p->ptrace_entry);
                release_task(p);
        }
+
+       write_lock_irq(&tasklist_lock);
 }
 
 int ptrace_readdata(struct task_struct *tsk, unsigned long src, char __user *dst, int len)