ptrace: ptrace_check_attach(): rename @kill to @ignore_state and add comments

PTRACE_INTERRUPT is going to be added which should also skip
task_is_traced() check in ptrace_check_attach().  Rename @kill to
@ignore_state and make it bool.  Add function comment while at it.

This patch doesn't introduce any behavior difference.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>

1 files changed, 19 insertions, 5 deletions

diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index 134f34cb142b..eb191116edf7 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -97,10 +97,24 @@ void __ptrace_unlink(struct task_struct *child)
         spin_unlock(&child->sighand->siglock);
 }
 
-/*
- * Check that we have indeed attached to the thing..
+/**
+ * ptrace_check_attach - check whether ptracee is ready for ptrace operation
+ * @child: ptracee to check for
+ * @ignore_state: don't check whether @child is currently %TASK_TRACED
+ *
+ * Check whether @child is being ptraced by %current and ready for further
+ * ptrace operations.  If @ignore_state is %false, @child also should be in
+ * %TASK_TRACED state and on return the child is guaranteed to be traced
+ * and not executing.  If @ignore_state is %true, @child can be in any
+ * state.
+ *
+ * CONTEXT:
+ * Grabs and releases tasklist_lock and @child->sighand->siglock.
+ *
+ * RETURNS:
+ * 0 on success, -ESRCH if %child is not ready.
  */
-int ptrace_check_attach(struct task_struct *child, int kill)
+int ptrace_check_attach(struct task_struct *child, bool ignore_state)
 {
         int ret = -ESRCH;
 
@@ -119,13 +133,13 @@ int ptrace_check_attach(struct task_struct *child, int kill)
                  */
                 spin_lock_irq(&child->sighand->siglock);
                 WARN_ON_ONCE(task_is_stopped(child));
-                if (task_is_traced(child) || kill)
+                if (task_is_traced(child) || ignore_state)
                         ret = 0;
                 spin_unlock_irq(&child->sighand->siglock);
         }
         read_unlock(&tasklist_lock);
 
-        if (!ret && !kill)
+        if (!ret && !ignore_state)
                 ret = wait_task_inactive(child, TASK_TRACED) ? 0 : -ESRCH;
 
         /* All systems go.. */