linux-kernel - Re: [PATCH 1/2] clocksource: imx-tpm: fix return -ETIME when delta exceeds INT

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Message-ID: <b88b6200-b92a-4cf3-946a-3c38cff886ec@linaro.org>
Date: Mon, 19 Aug 2024 15:21:36 +0200
From: Daniel Lezcano <daniel.lezcano@...aro.org>
To: Frank Li <Frank.Li@....com>, Thomas Gleixner <tglx@...utronix.de>,
 Shawn Guo <shawnguo@...nel.org>, Sascha Hauer <s.hauer@...gutronix.de>,
 Pengutronix Kernel Team <kernel@...gutronix.de>,
 Fabio Estevam <festevam@...il.com>, Dong Aisheng <aisheng.dong@....com>,
 "open list:CLOCKSOURCE, CLOCKEVENT DRIVERS" <linux-kernel@...r.kernel.org>,
 "open list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" <imx@...ts.linux.dev>,
 "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE"
 <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 1/2] clocksource: imx-tpm: fix return -ETIME when delta
 exceeds INT_MAX

On 25/07/2024 21:33, Frank Li wrote:
> From: Jacky Bai <ping.bai@....com>
> 
> In tpm_set_next_event(delta), return -ETIME by wrong cast to int when delta
> is larger than INT_MAX.

Is it something you observed or from your understanding of the code ?

> For example:
> 
> tpm_set_next_event(delta = 0xffff_fffe)
> {
>          ...
>          next = tpm_read_counter(); // assume next is 0x10
>          next += delta; // next will 0xffff_fffe + 0x10 = 0x1_0000_000e
>          now = tpm_read_counter();  // now is 0x10
>          ...
> 
>          return (int)(next - now) <= 0 ? -ETIME : 0;
>                       ^^^^^^^^^^
>                       0x1_0000_000e - 0x10 = 0xffff_fffe, which is -2 when
>                       cast to int. So return -ETIME.
> }
> 
> To fix this, introduce a 'prev' variable and check if 'now - prev' is
> larger than delta.
> 
> Cc: <stable@...r.kernel.org>
> Fixes: 059ab7b82eec ("clocksource/drivers/imx-tpm: Add imx tpm timer support")
> Signed-off-by: Jacky Bai <ping.bai@....com>
> Reviewed-by: Peng Fan <peng.fan@....com>
> Reviewed-by: Ye Li <ye.li@....com>
> Reviewed-by: Jason Liu <jason.hui.liu@....com>
> Signed-off-by: Frank Li <Frank.Li@....com>
> ---
>   drivers/clocksource/timer-imx-tpm.c | 8 ++++----
>   1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/clocksource/timer-imx-tpm.c b/drivers/clocksource/timer-imx-tpm.c
> index bd64a8a8427f3..cd23caf1e5999 100644
> --- a/drivers/clocksource/timer-imx-tpm.c
> +++ b/drivers/clocksource/timer-imx-tpm.c
> @@ -83,10 +83,10 @@ static u64 notrace tpm_read_sched_clock(void)
>   static int tpm_set_next_event(unsigned long delta,
>   				struct clock_event_device *evt)
>   {
> -	unsigned long next, now;
> +	unsigned long next, prev, now;
>   
> -	next = tpm_read_counter();
> -	next += delta;
> +	prev = tpm_read_counter();
> +	next = prev + delta;
>   	writel(next, timer_base + TPM_C0V);
>   	now = tpm_read_counter();
>   
> @@ -96,7 +96,7 @@ static int tpm_set_next_event(unsigned long delta,
>   	 * of writing CNT registers which may cause the min_delta event got
>   	 * missed, so we need add a ETIME check here in case it happened.
>   	 */
> -	return (int)(next - now) <= 0 ? -ETIME : 0;
> +	return (now - prev) >= delta ? -ETIME : 0;
>   }
>   
>   static int tpm_set_state_oneshot(struct clock_event_device *evt)


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