linux-kernel - Re: arch/mips/mm/tlbex.c:2243:3: warning: unannotated fall-through between switch labels

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Date:   Tue, 23 Nov 2021 00:52:30 -0800
From:   Joe Perches <joe@...ches.com>
To:     "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        kernel test robot <lkp@...el.com>
Cc:     llvm@...ts.linux.dev, kbuild-all@...ts.01.org,
        linux-kernel@...r.kernel.org, Kees Cook <keescook@...omium.org>,
        Nathan Chancellor <nathan@...nel.org>
Subject: Re: arch/mips/mm/tlbex.c:2243:3: warning: unannotated fall-through
 between switch labels

On Mon, 2021-11-22 at 18:55 -0600, Gustavo A. R. Silva wrote:
> On Tue, Nov 23, 2021 at 07:51:33AM +0800, kernel test robot wrote:
> > tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> > head:   136057256686de39cc3a07c2e39ef6bc43003ff6
> > commit: dee2b702bcf067d7b6b62c18bdd060ff0810a800 kconfig: Add support for -Wimplicit-fallthrough
> > date:   8 days ago
> > config: mips-randconfig-r016-20211116 (attached as .config)
> > compiler: clang version 14.0.0 (https://github.com/llvm/llvm-project fbe72e41b99dc7994daac300d208a955be3e4a0a)
> > reproduce (this is a W=1 build):
> >         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
> >         chmod +x ~/bin/make.cross
> >         # install mips cross compiling tool for clang build
> >         # apt-get install binutils-mips-linux-gnu
> >         # https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=dee2b702bcf067d7b6b62c18bdd060ff0810a800
> >         git remote add linus https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
> >         git fetch --no-tags linus master
> >         git checkout dee2b702bcf067d7b6b62c18bdd060ff0810a800
> >         # save the attached .config to linux build tree
> >         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 ARCH=mips 
> > 
> > If you fix the issue, kindly add following tag as appropriate
> > Reported-by: kernel test robot <lkp@...el.com>
> > 
> > All warnings (new ones prefixed by >>):
> > 
> > > > arch/mips/mm/tlbex.c:2243:3: warning: unannotated fall-through between switch labels [-Wimplicit-fallthrough]
> >                    case CPU_CAVIUM_OCTEON:
> >                    ^
> >    arch/mips/mm/tlbex.c:2243:3: note: insert 'break;' to avoid fall-through
> >                    case CPU_CAVIUM_OCTEON:
> >                    ^
> >                    break; 
> 
> I already have a patch for this here:
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/gustavoars/linux.git/commit/?h=for-linus/kspp&id=cd3ed04e7fc365e4e581333c3ff69c8da6ca0e8b

I think that's very odd looking code because of the braces.
And the fallthrough that you propose is odd as well.

Perhaps this would be better:
---
 arch/mips/mm/tlbex.c | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/arch/mips/mm/tlbex.c b/arch/mips/mm/tlbex.c
index b131e6a773832..a873e343d3dc9 100644
--- a/arch/mips/mm/tlbex.c
+++ b/arch/mips/mm/tlbex.c
@@ -2236,15 +2236,14 @@ static void build_r4000_tlb_load_handler(void)
 		uasm_i_tlbr(&p);
 
 		switch (current_cpu_type()) {
-		default:
-			if (cpu_has_mips_r2_exec_hazard) {
-				uasm_i_ehb(&p);
-
 		case CPU_CAVIUM_OCTEON:
 		case CPU_CAVIUM_OCTEON_PLUS:
 		case CPU_CAVIUM_OCTEON2:
-				break;
-			}
+			break;
+		default:
+			if (cpu_has_mips_r2_exec_hazard)
+				uasm_i_ehb(&p);
+			break;
 		}
 
 		/* Examine  entrylo 0 or 1 based on ptr. */