Re: [Y2038] [PATCH] hil_mlc: convert timeval to timespec64

[Arnd Bergmann <arnd@arndb.de>]

On Sunday 18 October 2015 17:45:19 WEN Pingbo wrote:
> Using struct timeval will cause time overflow in 2038, replacing it with
> a 64bit version.
> 
> In addition, the origin driver try to covert usec to jiffies manually in
> hilse_donode(). This is not a universal and safe way, using
> nsecs_to_jiffies() to fix that.
> 
> Signed-off-by: WEN Pingbo <pingbo.wen@linaro.org>

You should mention somewhere that you are also converting from real
time to monotonic time, and why this is done.

> ---
>  drivers/input/serio/hil_mlc.c    | 31 +++++++++++++++++--------------
>  drivers/input/serio/hp_sdc_mlc.c | 10 ++++++----
>  include/linux/hil_mlc.h          |  4 ++--
>  3 files changed, 25 insertions(+), 20 deletions(-)
> 
> diff --git a/drivers/input/serio/hil_mlc.c b/drivers/input/serio/hil_mlc.c
> index 65605e4..4e3b926 100644
> --- a/drivers/input/serio/hil_mlc.c
> +++ b/drivers/input/serio/hil_mlc.c
> @@ -274,14 +274,14 @@ static int hilse_match(hil_mlc *mlc, int unused)
>  /* An LCV used to prevent runaway loops, forces 5 second sleep when reset. */
>  static int hilse_init_lcv(hil_mlc *mlc, int unused)
>  {
> -	struct timeval tv;
> +	struct timespec64 ts64;
>  
> -	do_gettimeofday(&tv);
> +	ktime_get_ts64(&ts64);
>  
> -	if (mlc->lcv && (tv.tv_sec - mlc->lcv_tv.tv_sec) < 5)
> +	if (mlc->lcv && (ts64.tv_sec - mlc->lcv_ts64.tv_sec) < 5)
>  		return -1;
>  
> -	mlc->lcv_tv = tv;
> +	mlc->lcv_ts64 = ts64;
>  	mlc->lcv = 0;

No need to rename the two variables here. Also, it seems we never access the
tv_nsec portion at all, so this could use the simpler ktime_get_seconds()
or even 'jiffies' instead.

> @@ -605,7 +605,7 @@ static inline void hilse_setup_input(hil_mlc *mlc, const struct hilse_node *node
>  	}
>  	mlc->istarted = 1;
>  	mlc->intimeout = node->arg;
> -	do_gettimeofday(&(mlc->instart));
> +	ktime_get_ts64(&(mlc->instart));
>  	mlc->icount = 15;
>  	memset(mlc->ipacket, 0, 16 * sizeof(hil_packet));
>  	BUG_ON(down_trylock(&mlc->isem));

This looks unrelated to the change above, so I would suggest making separate patches.

> @@ -710,7 +710,7 @@ static int hilse_donode(hil_mlc *mlc)
>  			break;
>  		}
>  		mlc->ostarted = 0;
> -		do_gettimeofday(&(mlc->instart));
> +		ktime_get_ts64(&(mlc->instart));
>  		write_unlock_irqrestore(&mlc->lock, flags);
>  		nextidx = HILSEN_NEXT;
>  		break;
> @@ -731,18 +731,21 @@ static int hilse_donode(hil_mlc *mlc)
>  #endif
>  
>  	while (nextidx & HILSEN_SCHED) {
> -		struct timeval tv;
> +		struct timespec64 ts64;
>  
>  		if (!sched_long)
>  			goto sched;
>  
> -		do_gettimeofday(&tv);
> -		tv.tv_usec += USEC_PER_SEC * (tv.tv_sec - mlc->instart.tv_sec);
> -		tv.tv_usec -= mlc->instart.tv_usec;
> -		if (tv.tv_usec >= mlc->intimeout) goto sched;
> -		tv.tv_usec = (mlc->intimeout - tv.tv_usec) * HZ / USEC_PER_SEC;
> -		if (!tv.tv_usec) goto sched;
> -		mod_timer(&hil_mlcs_kicker, jiffies + tv.tv_usec);
> +		ktime_get_ts64(&ts64);
> +		ts64.tv_nsec += NSEC_PER_SEC *
> +			(ts64.tv_sec - mlc->instart.tv_sec);
> +		ts64.tv_nsec -= mlc->instart.tv_nsec;

tv_nsec will overflow here for any timeout over 4.3 seconds, where it
used to overflow after 4294 seconds. This is almost certainly a bug.

You could work around that by using ktime_get_ns() to get a nanosecond
value right away, but a 64-bit number is more expensive to convert to
jiffies.

> +		if (ts64.tv_nsec >= (mlc->intimeout * NSEC_PER_USEC))
> +			goto sched;
> +		ts64.tv_nsec = mlc->intimeout * NSEC_PER_USEC - ts64.tv_nsec;
> +		if (!ts64.tv_nsec) goto sched;

As you are modifying the line, you should also fix the coding style to
write

		if (!ts64.tv_nsec)
			goto sched;

I also notice that you modify the behavior here, by changing from
microsecond to nanosecond resolution, the equivalent of the original
would have been

		if (ts64.tv_nsec < NSECS_PER_USEC)


Your current version looks like it will practically never be true (meaning
you hit the exact nanosecond). Is this conditional actually needed at all
then? If it is, what is the intention and what should it be?

> +		mod_timer(&hil_mlcs_kicker,
> +				jiffies + nsecs_to_jiffies(ts64.tv_nsec));
>  		break;
>  	sched:
>  		tasklet_schedule(&hil_mlcs_tasklet);

This part seems like it would be easier to just use jiffies instead
of timspec64, to avoid having to convert it back.

> @@ -160,9 +160,11 @@ static int hp_sdc_mlc_in(hil_mlc *mlc, suseconds_t timeout)
>  			/* printk(KERN_DEBUG PREFIX ">[%x]\n", mlc->ipacket[0]); */
>  			goto wasup;
>  		}
> -		do_gettimeofday(&tv);
> -		tv.tv_usec += USEC_PER_SEC * (tv.tv_sec - mlc->instart.tv_sec);
> -		if (tv.tv_usec - mlc->instart.tv_usec > mlc->intimeout) {
> +		ktime_get_ts64(&ts64);
> +		ts64.tv_nsec += NSEC_PER_SEC *
> +			(ts64.tv_sec - mlc->instart.tv_sec);
> +		if (ts64.tv_nsec - mlc->instart.tv_nsec > mlc->intimeout *
> +				NSEC_PER_USEC) {
>  			/*	printk("!%i %i",
>  				tv.tv_usec - mlc->instart.tv_usec,
>  				mlc->intimeout);

same here.

	Arnd