Thread (4 messages) 4 messages, 3 authors, 2021-09-21

Re: [PATCH v2] livepatch: Fix idle cpu's tasks transition

From: Peter Zijlstra <peterz@infradead.org>
Date: 2021-09-21 17:43:34
Also in: lkml

On Wed, Sep 15, 2021 at 04:18:01PM +0200, Vasily Gorbik wrote:
quoted hunk ↗ jump to hunk
diff --git a/kernel/livepatch/transition.c b/kernel/livepatch/transition.c
index 291b857a6e20..2846a879f2dc 100644
--- a/kernel/livepatch/transition.c
+++ b/kernel/livepatch/transition.c
@@ -278,6 +278,8 @@ static int klp_check_stack(struct task_struct *task, char *err_buf)
  * 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
  * if the stack is unreliable, return false.
+ *
+ * Idle tasks are switched in the main loop when running.
  */
 static bool klp_try_switch_task(struct task_struct *task)
 {
@@ -308,6 +310,12 @@ static bool klp_try_switch_task(struct task_struct *task)
 	rq = task_rq_lock(task, &flags);
 
 	if (task_running(rq, task) && task != current) {
+		/*
+		 * Idle task might stay running for a long time. Switch them
+		 * in the main loop.
+		 */
+		if (is_idle_task(task))
+			resched_curr(rq);
 		snprintf(err_buf, STACK_ERR_BUF_SIZE,
 			 "%s: %s:%d is running\n", __func__, task->comm,
 			 task->pid);
So 'recently' we grew try_invoke_on_locked_down_task() (yes, that's a
crap name), and I'm thinking this code is very similar to that. So
perhaps we re-use that.

Perhaps have func() > 0 imply resched.

I'll have a play...
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