linux-kernel - Re: [patch 1/7] timers: Sanitize catchup_timer

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Message-ID: <20150527053919.GD31085@linux>
Date:	Wed, 27 May 2015 11:09:19 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Eric Dumazet <edumazet@...gle.com>,
	John Stultz <john.stultz@...aro.org>,
	Joonwoo Park <joonwoop@...eaurora.org>,
	Wenbo Wang <wenbo.wang@...blaze.com>
Subject: Re: [patch 1/7] timers: Sanitize catchup_timer_jiffies() usage

On 26-05-15, 22:50, Thomas Gleixner wrote:
> 3) __run_timers()
> 
>    We only check on entry, which is silly, because base->timer_jiffies
>    can be behind - especially on NOHZ kernels - and if there is a
>    single deferrable timer somewhere between base->timer_jiffies and
>    jiffies we expire it and then loop until base->timer_jiffies ==
>    jiffies.

This may be incorrect. Once we expire that single deferrable timer, we
call detach_expired_timer(), which calls catchup_timer_jiffies() at
its end. And so the following loop should end right away, isn't it ?

        while (time_after_eq(jiffies, base->timer_jiffies))

> +++ tip/kernel/time/timer.c
> -static bool catchup_timer_jiffies(struct tvec_base *base)
> +static inline bool catchup_timer_jiffies(struct tvec_base *base)

There is only one user left for this routine now, i.e. __run_timers().
Should we drop this routine ?

-- 
viresh
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