linux-kernel - [RFC PATCH 3/3] lockdep: Briefly comment current->hardirq

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Date:   Mon, 23 Mar 2020 04:32:07 +0100
From:   Frederic Weisbecker <frederic@...nel.org>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     Frederic Weisbecker <frederic@...nel.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: [RFC PATCH 3/3] lockdep: Briefly comment current->hardirq_threadable usecases

We have yet to find a proper comment for rcu_iw_handler() though.

Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc: Paul E. McKenney <paulmck@...nel.org>
---
 kernel/time/posix-cpu-timers.c | 1 +
 kernel/time/tick-sched.c       | 4 ++++
 2 files changed, 5 insertions(+)

diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c
index d29a06d60206..85902d756e21 100644
--- a/kernel/time/posix-cpu-timers.c
+++ b/kernel/time/posix-cpu-timers.c
@@ -1126,6 +1126,7 @@ void run_posix_cpu_timers(void)
 	if (!fastpath_timer_check(tsk))
 		return;
 
+	/* Should be offloaded to task_work at some future */
 	trace_hardirq_threadable();
 	if (!lock_task_sighand(tsk, &flags)) {
 		trace_hardirq_unthreadable();
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 3e2dc9b8858c..d469972673e4 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -245,6 +245,10 @@ static void nohz_full_kick_func(struct irq_work *work)
 
 static DEFINE_PER_CPU(struct irq_work, nohz_full_kick_work) = {
 	.func = nohz_full_kick_func,
+	/*
+	 * Must stay in hardirq. Threading would mess up with tick
+	 * dependencies.
+	 */
 	.flags = ATOMIC_INIT(IRQ_WORK_HARD_IRQ),
 };
 
-- 
2.25.0