linux-kernel - Re: [PATCH V2] hrtimer: Printing timer info when hitting BUG

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Date:	Tue, 06 Nov 2012 09:07:27 +0800
From:	Yanmin Zhang <yanmin_zhang@...ux.intel.com>
To:	Chuansheng Liu <chuansheng.liu@...el.com>
Cc:	tglx@...utronix.de, mingo@...nel.org, a.p.zijlstra@...llo.nl,
	linux-kernel@...r.kernel.org, fei.li@...el.com
Subject: Re: [PATCH V2] hrtimer: Printing timer info when hitting BUG_ON()

On Tue, 2012-10-30 at 18:27 +0800, Chuansheng Liu wrote:
> We encounted one BUG_ON() issue at function __run_hrtimer(),
> but the panic info is not enough to find out which hrtimer
> users use the hrtimer wrongly.
> (in this BUG_ON case, it is callback running at the same time
> hrtimer_start() is executed on different context.)
> 
> We can print basic timer info before BUG(), it is easy to find
> out which hrtimer user has fault, the output info is like below:
> 
> <3>[   41.118552] timer info: state/3, func/test_timer_cb
> <3>[   41.118618] timer stats: pid/786(sh), site/hrtimer_start
> <0>[   41.118670] ------------[ cut here ]------------
> <2>[   41.118691] kernel BUG at /root/r4_code/hardware/intel/linux-2.6/kernel/hrtimer.c:1260!
> <0>[   41.118715] invalid opcode: 0000 [#1] PREEMPT SMP
> 
> The infos of callback/state are very helpful for debugging this BUG_ON().
It's a useful patch.

Thomas,

Could you merge it into your testing tree, so other developers could also
benefit from it?

Thanks all.
Yanmin

> 
> Signed-off-by: Li Fei <fei.li@...el.com>
> Signed-off-by: liu chuansheng <chuansheng.liu@...el.com>
> ---
>  kernel/hrtimer.c |   21 ++++++++++++++++++++-
>  1 files changed, 20 insertions(+), 1 deletions(-)
> 
> diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c
> index 6db7a5e..0618eaf 100644
> --- a/kernel/hrtimer.c
> +++ b/kernel/hrtimer.c
> @@ -1204,6 +1204,22 @@ int hrtimer_get_res(const clockid_t which_clock, struct timespec *tp)
>  }
>  EXPORT_SYMBOL_GPL(hrtimer_get_res);
>  
> +/*
> + * dump_hrtimer_callinfo - print hrtimer information including:
> + * state, callback function, pid and start_site.
> +*/
> +static void dump_hrtimer_callinfo(struct hrtimer *timer)
> +{
> +
> +	pr_err("timer info: state/%lx, func/%pf\n",
> +		timer->state, timer->function);
> +
> +#ifdef CONFIG_TIMER_STATS
> +	pr_err("timer stats: pid/%d(%s), site/%pf\n",
> +		timer->start_pid, timer->start_comm, timer->start_site);
> +#endif
> +}
> +
>  static void __run_hrtimer(struct hrtimer *timer, ktime_t *now)
>  {
>  	struct hrtimer_clock_base *base = timer->base;
> @@ -1235,7 +1251,10 @@ static void __run_hrtimer(struct hrtimer *timer, ktime_t *now)
>  	 * hrtimer_start_range_ns() or in hrtimer_interrupt()
>  	 */
>  	if (restart != HRTIMER_NORESTART) {
> -		BUG_ON(timer->state != HRTIMER_STATE_CALLBACK);
> +		if (timer->state != HRTIMER_STATE_CALLBACK) {
> +			dump_hrtimer_callinfo(timer);
> +			BUG();
> +		}
>  		enqueue_hrtimer(timer, base);
>  	}
>  


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