linux-kernel - Re: [PATCH 2/5] clocksource: Allow clocksource_mark

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Message-ID: <20180423164325.GR4129@hirez.programming.kicks-ass.net>
Date:   Mon, 23 Apr 2018 18:43:25 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     tglx@...utronix.de
Cc:     linux-kernel@...r.kernel.org, diego.viola@...il.com,
        len.brown@...el.com, rjw@...ysocki.net, rui.zhang@...el.com
Subject: Re: [PATCH 2/5] clocksource: Allow clocksource_mark_unstable() on
 unregisered clocksources

On Mon, Apr 23, 2018 at 06:41:13PM +0200, Peter Zijlstra wrote:
> I've no idea why it says it cannot do that with the lock held. But
> there's more stale comments in there.

Like that one, the x86 tsc code is the only caller of this. I could not
find anything hotplug.

--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -173,10 +173,8 @@ static void __clocksource_unstable(struc
  * clocksource_mark_unstable - mark clocksource unstable via watchdog
  * @cs:		clocksource to be marked unstable
  *
- * This function is called instead of clocksource_change_rating from
- * cpu hotplug code to avoid a deadlock between the clocksource mutex
- * and the cpu hotplug mutex. It defers the update of the clocksource
- * to the watchdog thread.
+ * This function is called by the x86 TSC code to mark clocksources as unstable;
+ * it defers demotion and re-selection to a kthread.
  */
 void clocksource_mark_unstable(struct clocksource *cs)
 {