linux-kernel - [tip:timers/core] hrtimer: Correct blatantly incorrect comment

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Date:   Mon, 15 Jan 2018 19:40:51 -0800
From:   tip-bot for Thomas Gleixner <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     peterz@...radead.org, frederic@...nel.org, hpa@...or.com,
        mingo@...nel.org, torvalds@...ux-foundation.org,
        anna-maria@...utronix.de, hch@....de, tglx@...utronix.de,
        john.stultz@...aro.org, linux-kernel@...r.kernel.org
Subject: [tip:timers/core] hrtimer: Correct blatantly incorrect comment

Commit-ID:  d05ca13b8d3f685667b3b1748fa89285466270c5
Gitweb:     https://git.kernel.org/tip/d05ca13b8d3f685667b3b1748fa89285466270c5
Author:     Thomas Gleixner <tglx@...utronix.de>
AuthorDate: Thu, 21 Dec 2017 11:41:31 +0100
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Tue, 16 Jan 2018 02:35:44 +0100

hrtimer: Correct blatantly incorrect comment

The protection of a hrtimer which runs its callback against migration to a
different CPU has nothing to do with hard interrupt context.

The protection against migration of a hrtimer running the expiry callback
is the pointer in the cpu_base which holds a pointer to the currently
running timer. This pointer is evaluated in the code which potentially
switches the timer base and makes sure it's kept on the CPU on which the
callback is running.

Reported-by: Anna-Maria Gleixner <anna-maria@...utronix.de>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Anna-Maria Gleixner <anna-maria@...utronix.de>
Reviewed-by: Frederic Weisbecker <frederic@...nel.org>
Cc: Christoph Hellwig <hch@....de>
Cc: John Stultz <john.stultz@...aro.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: keescook@...omium.org
Link: http://lkml.kernel.org/r/20171221104205.7269-3-anna-maria@linutronix.de
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 kernel/time/hrtimer.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index 1d06d2b..7687355 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -1195,9 +1195,9 @@ static void __run_hrtimer(struct hrtimer_cpu_base *cpu_base,
 		timer->is_rel = false;
 
 	/*
-	 * Because we run timers from hardirq context, there is no chance
-	 * they get migrated to another cpu, therefore its safe to unlock
-	 * the timer base.
+	 * The timer is marked as running in the CPU base, so it is
+	 * protected against migration to a different CPU even if the lock
+	 * is dropped.
 	 */
 	raw_spin_unlock(&cpu_base->lock);
 	trace_hrtimer_expire_entry(timer, now);