Re: [PATCH] jiffies: Cast to unsigned long for secs_to_jiffies() conversion

[David Laight <david.laight.linux@gmail.com>]

On Thu, 30 Jan 2025 18:43:17 +0000
Easwar Hariharan <eahariha@linux.microsoft.com> wrote:

> While converting users of msecs_to_jiffies(), lkp reported that some
> range checks would always be true because of the mismatch between the
> implied int value of secs_to_jiffies() vs the unsigned long
> return value of the msecs_to_jiffies() calls it was replacing. Fix this
> by casting secs_to_jiffies() values as unsigned long.

Surely 'unsigned long' can't be the right type ?
It changes between 32bit and 64bit systems.
Either it is allowed to wrap - so should be 32bit on both,
or wrapping is unexpected and it needs to be 64bit on both.

As we all know (to our cost in many cases) a ms counter wraps 32bit in
about 48 days.

	David

> 
> Fixes: b35108a51cf7ba ("jiffies: Define secs_to_jiffies()")
> CC: stable@vger.kernel.org # 6.12+
> CC: Andrew Morton <akpm@linux-foundation.org>
> Reported-by: kernel test robot <lkp@intel.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202501301334.NB6NszQR-lkp@intel.com/
> Signed-off-by: Easwar Hariharan <eahariha@linux.microsoft.com>
> ---
>  include/linux/jiffies.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/linux/jiffies.h b/include/linux/jiffies.h
> index ed945f42e064..0ea8c9887429 100644
> --- a/include/linux/jiffies.h
> +++ b/include/linux/jiffies.h
> @@ -537,7 +537,7 @@ static __always_inline unsigned long msecs_to_jiffies(const unsigned int m)
>   *
>   * Return: jiffies value
>   */
> -#define secs_to_jiffies(_secs) ((_secs) * HZ)
> +#define secs_to_jiffies(_secs) (unsigned long)((_secs) * HZ)
>  
>  extern unsigned long __usecs_to_jiffies(const unsigned int u);
>  #if !(USEC_PER_SEC % HZ)