linux-kernel - Re: [PATCH] prevent timespec/timeval to ktime

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Date:	Thu, 31 Aug 2006 20:46:12 -0700
From:	Andrew Morton <akpm@...l.org>
To:	tglx@...utronix.de
Cc:	Ingo Molnar <mingo@...e.hu>, LKML <linux-kernel@...r.kernel.org>,
	Frank v Waveren <fvw@....cx>
Subject: Re: [PATCH] prevent timespec/timeval to ktime_t overflow

On Wed, 30 Aug 2006 10:44:28 +0200
Thomas Gleixner <tglx@...utronix.de> wrote:

> Frank v. Waveren pointed out that on 64bit machines the timespec to
> ktime_t conversion might overflow. This is also true for timeval to
> ktime_t conversions. This breaks a "sleep inf" on 64bit machines.
> 
> While a timespec/timeval with tx.sec = MAX_LONG is valid by
> specification the internal representation of ktime_t is based on
> nanoseconds. The conversion of seconds to nanoseconds overflows for
> seconds values >= (MAX_LONG / NSEC_PER_SEC).
> 
> Check the seconds argument to the conversion and limit it to the maximum
> time which can be represented by ktime_t.
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> 
> diff --git a/include/linux/ktime.h b/include/linux/ktime.h
> index ed3396d..1beafb3 100644
> --- a/include/linux/ktime.h
> +++ b/include/linux/ktime.h
> @@ -57,6 +57,7 @@ typedef union {
>  } ktime_t;
>  
>  #define KTIME_MAX			(~((u64)1 << 63))
> +#define KTIME_SEC_MAX			(KTIME_MAX / NSEC_PER_SEC)
>  
>  /*
>   * ktime_t definitions when using the 64-bit scalar representation:
> @@ -73,6 +74,10 @@ typedef union {
>   */
>  static inline ktime_t ktime_set(const long secs, const unsigned long nsecs)
>  {
> +#if (BITS_PER_LONG == 64)
> +	if (unlikely(secs >= KTIME_SEC_MAX))
> +		return (ktime_t){ .tv64 = KTIME_MAX };
> +#endif
>  	return (ktime_t) { .tv64 = (s64)secs * NSEC_PER_SEC + (s64)nsecs };
>  }
>  

This makes my FC3 x86_64 testbox hang during udev startup.  sysrq-T trace at
http://www.zip.com.au/~akpm/linux/patches/stuff/log-x.

I had a quick look at the args to hrtimer_nanosleep and all seems to be in
order.
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