linux-kernel - Re: [PATCH net-next] net: ipa: always inline ipa_aggr_granularity

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Date:   Wed, 11 Aug 2021 15:02:38 +0300
From:   Leon Romanovsky <leon@...nel.org>
To:     Alex Elder <elder@...aro.org>
Cc:     davem@...emloft.net, kuba@...nel.org, bjorn.andersson@...aro.org,
        evgreen@...omium.org, cpratapa@...eaurora.org,
        subashab@...eaurora.org, lkp@...el.com, elder@...nel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next] net: ipa: always inline
 ipa_aggr_granularity_val()

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@...el.com>
> Signed-off-by: Alex Elder <elder@...aro.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.

Thanks

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