Merge branch 'linus' into release

Conflicts:
	drivers/acpi/debug.c

Signed-off-by: Len Brown <len.brown@intel.com>

1 files changed, 9 insertions, 3 deletions

diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index 74a3d693c196..f34d798ef4a2 100644
--- 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)