linux-kernel - Re: [PATCH 2/2] timer: Make sure TIMER_FLAG

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Date:	Fri, 28 Feb 2014 11:52:45 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Viresh Kumar <viresh.kumar@...aro.org>
cc:	linaro-kernel@...ts.linaro.org, linux-kernel@...r.kernel.org,
	fweisbec@...il.com, tj@...nel.org, peterz@...radead.org,
	mingo@...nel.org
Subject: Re: [PATCH 2/2] timer: Make sure TIMER_FLAG_MASK bits are free in
 allocated base

On Fri, 28 Feb 2014, Viresh Kumar wrote:

> Currently we are using two lowest bit of base for internal purpose and so they
> both should be zero in the allocated address. The code was doing the right thing
> before this patch came in:
> 
> commit c5f66e99b7cb091e3d51ae8e8156892e8feb7fa3
> Author: Tejun Heo <tj@...nel.org>
> Date:   Wed Aug 8 11:10:28 2012 -0700
> 
>     timer: Implement TIMER_IRQSAFE
> 
> Tejun probably forgot to update this piece of code which checks if the lowest
> 'n' bits are zero or not and so wasn't updated according to the new flag. Lets
> use TIMER_FLAG_MASK in the calculations here, so that this code wouldn't require
> a change later on with another flag in.

Are you planning to introduce more flag horror? Don't go there. The
timer_list code is about to be rewritten completely and I'm not going
to add new features to the existing code base.

> Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
> ---
>  kernel/timer.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/timer.c b/kernel/timer.c
> index e8e7839..d52a8ff 100644
> --- a/kernel/timer.c
> +++ b/kernel/timer.c
> @@ -1548,9 +1548,8 @@ static int init_timers_cpu(int cpu)
>  			if (!base)
>  				return -ENOMEM;
>  
> -			/* Make sure that tvec_base is 2 byte aligned */
> -			if (tbase_get_deferrable(base)) {
> -				WARN_ON(1);
> +			/* Make sure tvec_base has TIMER_FLAG_MASK bits free */
> +			if (WARN_ON(base != tbase_get_base(base))) {
>  				kfree(base);
>  				return -ENOMEM;
>  			}
> -- 
> 1.7.12.rc2.18.g61b472e
> 
> 
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