linux-kernel - Re: [PATCH 5.2 083/215] net/ipv4: fib_trie: Avoid cryptic ternary expressions

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Message-ID: <20190729205422.GH250418@google.com>
Date:   Mon, 29 Jul 2019 13:54:22 -0700
From:   Matthias Kaehlcke <mka@...omium.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Douglas Anderson <dianders@...omium.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Alexander Duyck <alexander.h.duyck@...ux.intel.com>,
        "David S. Miller" <davem@...emloft.net>,
        Sasha Levin <sashal@...nel.org>,
        Toralf Förster <toralf.foerster@....de>,
        Nathan Huckleberry <nhuck@...gle.com>
Subject: Re: [PATCH 5.2 083/215] net/ipv4: fib_trie: Avoid cryptic ternary
 expressions

Hi Greg,

Toralf just pointed out in another thread that the commit message and
the content of this patch don't match (https://lkml.org/lkml/2019/7/29/1475)

I did some minor digging, the content of the queued patch is:

commit 4df607cc6fe8e46b258ff2a53d0a60ca3008ffc7
Author: Nathan Huckleberry <nhuck@...gle.com>
Date:   Mon Jun 17 10:28:29 2019 -0700

    kbuild: Remove unnecessary -Wno-unused-value


however the commit message is from:

commit 25cec756891e8733433efea63b2254ddc93aa5cc
Author: Matthias Kaehlcke <mka@...omium.org>
Date:   Tue Jun 18 14:14:40 2019 -0700

    net/ipv4: fib_trie: Avoid cryptic ternary expressions


It seems this hasn't been commited to -stable yet, so we are probably
in time to remove it from the queue before it becomes git history and
have Nathan re-spin the patch(es).

On Mon, Jul 29, 2019 at 09:21:19PM +0200, Greg Kroah-Hartman wrote:
> [ Upstream commit 25cec756891e8733433efea63b2254ddc93aa5cc ]
> 
> empty_child_inc/dec() use the ternary operator for conditional
> operations. The conditions involve the post/pre in/decrement
> operator and the operation is only performed when the condition
> is *not* true. This is hard to parse for humans, use a regular
> 'if' construct instead and perform the in/decrement separately.
> 
> This also fixes two warnings that are emitted about the value
> of the ternary expression being unused, when building the kernel
> with clang + "kbuild: Remove unnecessary -Wno-unused-value"
> (https://lore.kernel.org/patchwork/patch/1089869/):
> 
> CC      net/ipv4/fib_trie.o
> net/ipv4/fib_trie.c:351:2: error: expression result unused [-Werror,-Wunused-value]
>         ++tn_info(n)->empty_children ? : ++tn_info(n)->full_children;
> 
> Fixes: 95f60ea3e99a ("fib_trie: Add collapse() and should_collapse() to resize")
> Signed-off-by: Matthias Kaehlcke <mka@...omium.org>
> Reviewed-by: Douglas Anderson <dianders@...omium.org>
> Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>
> Acked-by: Alexander Duyck <alexander.h.duyck@...ux.intel.com>
> Signed-off-by: David S. Miller <davem@...emloft.net>
> Signed-off-by: Sasha Levin <sashal@...nel.org>
> ---
>  scripts/Makefile.extrawarn | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/scripts/Makefile.extrawarn b/scripts/Makefile.extrawarn
> index 3ab8d1a303cd..b293246e48fe 100644
> --- a/scripts/Makefile.extrawarn
> +++ b/scripts/Makefile.extrawarn
> @@ -68,7 +68,6 @@ else
>  
>  ifdef CONFIG_CC_IS_CLANG
>  KBUILD_CFLAGS += -Wno-initializer-overrides
> -KBUILD_CFLAGS += -Wno-unused-value
>  KBUILD_CFLAGS += -Wno-format
>  KBUILD_CFLAGS += -Wno-sign-compare
>  KBUILD_CFLAGS += -Wno-format-zero-length