Re: [RFC][PATCH 3/7] sched,livepatch: Use task_try_func()

Instead of frobbing around with scheduler internals, use the shiny new
task_try_func() interface.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 kernel/livepatch/transition.c |   84 ++++++++++++++++++------------------------
 1 file changed, 37 insertions(+), 47 deletions(-)

--- a/kernel/livepatch/transition.c
+++ b/kernel/livepatch/transition.c

@@ -274,6 +266,22 @@ static int klp_check_stack(struct task_s
 	return 0;
 }
 
+static int klp_check_task(struct task_struct *task, void *arg)

+{
+	int ret;
+
+	if (task_curr(task))
+		return -EBUSY;
+
+	ret = klp_check_stack(task, arg);
+	if (ret)
+		return ret;
+
+	clear_tsk_thread_flag(task, TIF_PATCH_PENDING);
+	task->patch_state = klp_target_state;
+	return 0;
+}
+
 /*
  * Try to safely switch a task to the target patch state.  If it's currently
  * running, or it's sleeping on a to-be-patched or to-be-unpatched function, or

@@ -305,36 +308,23 @@ static bool klp_try_switch_task(struct t
 	 * functions.  If all goes well, switch the task to the target patch
 	 * state.
 	 */
-	rq = task_rq_lock(task, &flags);
-
-	if (task_running(rq, task) && task != current) {
-		snprintf(err_buf, STACK_ERR_BUF_SIZE,
-			 "%s: %s:%d is running\n", __func__, task->comm,
-			 task->pid);
-		goto done;
+	ret = task_try_func(task, klp_check_task, &old_name);
+	switch (ret) {
+	case -EBUSY:
+		pr_debug("%s: %s:%d is running\n",
+			 __func__, task->comm, task->pid);
+		break;
+	case -EINVAL:
+		pr_debug("%s: %s:%d has an unreliable stack\n",
+			 __func__, task->comm, task->pid);
+		break;
+	case -EADDRINUSE:
+		pr_debug("%s: %s:%d is sleeping on function %s\n",
+			 __func__, task->comm, task->pid, old_name);
+		break;

 	}
 
-	ret = klp_check_stack(task, err_buf);
-	if (ret)
-		goto done;
-
-	success = true;
-
-	clear_tsk_thread_flag(task, TIF_PATCH_PENDING);
-	task->patch_state = klp_target_state;
-
-done:
-	task_rq_unlock(rq, task, &flags);
-
-	/*
-	 * Due to console deadlock issues, pr_debug() can't be used while
-	 * holding the task rq lock.  Instead we have to use a temporary buffer
-	 * and print the debug message after releasing the lock.
-	 */
-	if (err_buf[0] != '\0')
-		pr_debug("%s", err_buf);
-
-	return success;
+	return !ret;
 }