linux-kernel - Re: [PATCH] posix-timers: CLOCK_MONOTONIC_RAW: fix the usage of ->it

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Date:	Sat, 20 Dec 2008 21:10:33 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Oleg Nesterov <oleg@...hat.com>
cc:	Eric Sesterhenn <snakebyte@....de>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] posix-timers: CLOCK_MONOTONIC_RAW: fix the usage of
 ->it_clock

On Sat, 20 Dec 2008, Oleg Nesterov wrote:

> (compile tested)
> 
> common_timer_create() and common_timer_set() blindly pass ->it_clock to
> hrtimer_init() as clock_id. This used to work until CLOCK_MONOTONIC_RAW
> was introduced, now we should be careful.
> 
> Perhaps it makes sense to add BUG_ON(clock_id >= HRTIMER_MAX_CLOCK_BASES)
> to __hrtimer_init(), the wrong clock_id leads to catastrophe.
> 
> Reported-by: Eric Sesterhenn <snakebyte@....de>
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>
> 
> --- K-28/kernel/posix-timers.c~CLOCK_MONOTONIC_RAW	2008-12-02 17:12:40.000000000 +0100
> +++ K-28/kernel/posix-timers.c	2008-12-20 18:23:28.000000000 +0100
> @@ -191,12 +191,20 @@ static inline int common_clock_set(const
>  	return do_sys_settimeofday(tp, NULL);
>  }
>  
> -static int common_timer_create(struct k_itimer *new_timer)
> +static inline int
> +__common_timer_init(struct k_itimer *timer, enum hrtimer_mode mode)
>  {
> -	hrtimer_init(&new_timer->it.real.timer, new_timer->it_clock, 0);
> +	clockid_t clock_id = timer->it_clock ?
> +				CLOCK_MONOTONIC : CLOCK_REALTIME;
> +	hrtimer_init(&timer->it.real.timer, clock_id, mode);
>  	return 0;
>  }

No, this is wrong. We do not want to create a timer for
CLOCK_MONOTONIC_RAW.

	tglx
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