linux-kernel - [RFC][PATCH 5/7] sched,livepatch: Use wake_up_if

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Message-ID: <20210922110836.185239814@infradead.org>
Date:   Wed, 22 Sep 2021 13:05:11 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     gor@...ux.ibm.com, jpoimboe@...hat.com, jikos@...nel.org,
        mbenes@...e.cz, pmladek@...e.com, mingo@...nel.org
Cc:     linux-kernel@...r.kernel.org, peterz@...radead.org,
        joe.lawrence@...hat.com, fweisbec@...il.com, tglx@...utronix.de,
        hca@...ux.ibm.com, svens@...ux.ibm.com, sumanthk@...ux.ibm.com,
        live-patching@...r.kernel.org, paulmck@...nel.org
Subject: [RFC][PATCH 5/7] sched,livepatch: Use wake_up_if_idle()

Make sure to prod idle CPUs so they call klp_update_patch_state().

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 kernel/livepatch/transition.c |   16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

--- a/kernel/livepatch/transition.c
+++ b/kernel/livepatch/transition.c
@@ -287,21 +287,21 @@ static int klp_check_task(struct task_st
  * running, or it's sleeping on a to-be-patched or to-be-unpatched function, or
  * if the stack is unreliable, return false.
  */
-static bool klp_try_switch_task(struct task_struct *task)
+static int klp_try_switch_task(struct task_struct *task)
 {
 	const char *old_name;
 	int ret;
 
 	/* check if this task has already switched over */
 	if (task->patch_state == klp_target_state)
-		return true;
+		return 0;
 
 	/*
 	 * For arches which don't have reliable stack traces, we have to rely
 	 * on other methods (e.g., switching tasks at kernel exit).
 	 */
 	if (!klp_have_reliable_stack())
-		return false;
+		return -EINVAL;
 
 	/*
 	 * Now try to check the stack for any to-be-patched or to-be-unpatched
@@ -324,7 +324,7 @@ static bool klp_try_switch_task(struct t
 		break;
 	}
 
-	return !ret;
+	return ret;
 }
 
 /*
@@ -394,7 +394,7 @@ void klp_try_complete_transition(void)
 	 */
 	read_lock(&tasklist_lock);
 	for_each_process_thread(g, task)
-		if (!klp_try_switch_task(task))
+		if (klp_try_switch_task(task))
 			complete = false;
 	read_unlock(&tasklist_lock);
 
@@ -405,8 +405,10 @@ void klp_try_complete_transition(void)
 	for_each_possible_cpu(cpu) {
 		task = idle_task(cpu);
 		if (cpu_online(cpu)) {
-			if (!klp_try_switch_task(task))
-				complete = false;
+			int ret = klp_try_switch_task(task);
+			if (ret == -EBUSY)
+				wake_up_if_idle(cpu);
+			complete = !ret;
 		} else if (task->patch_state != klp_target_state) {
 			/* offline idle tasks can be switched immediately */
 			clear_tsk_thread_flag(task, TIF_PATCH_PENDING);