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Date: Mon, 13 Jun 2016 16:36:48 +0200
From: Richard Cochran <richardcochran@gmail.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: LKML <linux-kernel@vger.kernel.org>, Ingo Molnar <mingo@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Eric Dumazet <edumazet@google.com>,
        Frederic Weisbecker <fweisbec@gmail.com>, Chris Mason <clm@fb.com>,
        Arjan van de Ven <arjan@infradead.org>, rt@linutronix.de
Subject: Re: [patch 13/20] timer: Switch to a non cascading wheel
Message-ID: <20160613143647.GA17907@localhost.localdomain>
References: <20160613070440.950649741@linutronix.de>
 <20160613075929.282143900@linutronix.de>
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On Mon, Jun 13, 2016 at 08:41:00AM -0000, Thomas Gleixner wrote:
> +static inline struct timer_base *get_timer_base(u32 tflags)
> +{
> +	return get_timer_cpu_base(tflags, tflags & TIMER_BASEMASK);
> +}

This should rather be (tflags & TIMER_CPUMASK) to avoid using
per_cpu_ptr() with the TIMER_MIGRATING bit set in the CPU index.

The one caller in this patch is okay, since it already checks that
TIMER_MIGRATING is clear:

>  static struct timer_base *lock_timer_base(struct timer_list *timer,
> -					unsigned long *flags)
> +					  unsigned long *flags)
>  	__acquires(timer->base->lock)
>  {
>  	for (;;) {
> -		u32 tf = timer->flags;
>  		struct timer_base *base;
> +		u32 tf = timer->flags;
>  
>  		if (!(tf & TIMER_MIGRATING)) {
> -			base = per_cpu_ptr(&timer_bases, tf & TIMER_CPUMASK);
> +			base = get_timer_base(tf);

However, in patch #20, we'll have this in __mod_timer();

		/*
		 * Take the current timer_jiffies of base, but without holding
		 * the lock!
		 */
		base = get_timer_base(timer->flags);

Thanks,
Richard