Re: [PATCH net-next] net: ipa: always inline ipa_aggr_granularity_val()

Leon Romanovsky
2021-08-11T12:12:55Z

On Wed, Aug 11, 2021 at 07:06:01AM -0500, Alex Elder wrote:
> On 8/11/21 7:02 AM, Leon Romanovsky wrote:
> > On Tue, Aug 10, 2021 at 11:02:13AM -0500, Alex Elder wrote:
> >> It isn't required, but all callers of ipa_aggr_granularity_val()
> >> pass a constant value (IPA_AGGR_GRANULARITY) as the usec argument.
> >> Two of those callers are in ipa_validate_build(), with the result
> >> being passed to BUILD_BUG_ON().
> >>
> >> Evidently the "sparc64-linux-gcc" compiler (at least) doesn't always
> >> inline ipa_aggr_granularity_val(), so the result of the function is
> >> not constant at compile time, and that leads to build errors.
> >>
> >> Define the function with the __always_inline attribute to avoid the
> >> errors. And given that the function is inline, we can switch the
> >> WARN_ON() there to be BUILD_BUG_ON().
> >>
> >> Fixes: 5bc5588466a1f ("net: ipa: use WARN_ON() rather than assertions")
> >> Reported-by: kernel test robot <lkp@intel.com>
> >> Signed-off-by: Alex Elder <elder@linaro.org>
> >> ---
> >>
> >> David/Jakub, this fixes a bug in a commit in net-next/master. -Alex
> >>
> >> drivers/net/ipa/ipa_main.c | 4 ++--
> >> 1 file changed, 2 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/drivers/net/ipa/ipa_main.c b/drivers/net/ipa/ipa_main.c
> >> index 25bbb456e0078..f90b3521e266b 100644
> >> --- a/drivers/net/ipa/ipa_main.c
> >> +++ b/drivers/net/ipa/ipa_main.c
> >> @@ -255,9 +255,9 @@ ipa_hardware_config_qsb(struct ipa *ipa, const struct ipa_data *data)
> >> * less than the number of timer ticks in the requested period. 0 is not
> >> * a valid granularity value.
> >> */
> >> -static u32 ipa_aggr_granularity_val(u32 usec)
> >> +static __always_inline u32 ipa_aggr_granularity_val(u32 usec)
> >> {
> >> - WARN_ON(!usec);
> >> + BUILD_BUG_ON(!usec);
> >
> > So what exactly are you checking here if all callers pass same value?
> > It is in-kernel API, declared as static inside one module. There is no
> > need to protect from itself.
>
> Yeah that's a good point. It can just as well be removed.
> I think the check was added before I knew it was only going
> to be used with a single constant value. That said, the
> point was to check at runtime a required constraint.
>
> I'll post version 2 that simply removes it. Thanks.

Thanks
>
> -Alex
>
> >
> > Thanks
> >
> >>
> >> return DIV_ROUND_CLOSEST(usec * TIMER_FREQUENCY, USEC_PER_SEC) - 1;
> >> }
> >> --
> >> 2.27.0
> >>
>