Re: [PATCH] [RFC] time: Make sure jiffies_to_msecs() preserves non-zero time periods

[Arnd Bergmann]

On Tue, Nov 14, 2017 at 6:36 PM, Geert Uytterhoeven
<geert@xxxxxxxxxxxxxx> wrote:
> For the common cases where 1000 is a multiple of HZ, or HZ is a multiple
> of 1000, jiffies_to_msecs() never returns zero when passed a non-zero
> time period.
>
> However, if HZ > 1000 and not an integer multiple of 1000 (e.g. 2001),
> jiffies_to_msecs() may return zero for small non-zero time periods.
> This may break code that relies on receiving back a non-zero value, e.g.
> drivers/char/tpm/tpm2-cmd.c:tpm2_do_selftest().

For reference, there are exactly three platforms that allow HZ to be larger
than 1000, and they specifically use HZ=1024: alpha, itanium and
mips/decstation.

> With the fix above, this becomes a false positive.
> Nevertheless, it may be a good idea to preinitialize rc anyway, but I
> have no idea what's the correct value (else I would have sent a patch
> to do so ;-).

I think changing the while() loop into do{}while() would be appropriate here.

      Arnd