linux-kernel - [PATCH v2] nfs: remove incorrect fallthrough label

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Message-Id: <20200916200255.1382086-1-ndesaulniers@google.com>
Date:   Wed, 16 Sep 2020 13:02:55 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Trond Myklebust <trond.myklebust@...merspace.com>,
        Anna Schumaker <anna.schumaker@...app.com>
Cc:     "Gustavo A . R . Silva" <gustavo@...eddedor.com>,
        Joe Perches <joe@...ches.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nathan Chancellor <natechancellor@...il.com>,
        Hongxiang Lou <louhongxiang@...wei.com>,
        Miaohe Lin <linmiaohe@...wei.com>, linux-nfs@...r.kernel.org,
        linux-kernel@...r.kernel.org, clang-built-linux@...glegroups.com
Subject: [PATCH v2] nfs: remove incorrect fallthrough label

There is no case after the default from which to fallthrough to. Clang
will error in this case (unhelpfully without context, see link below)
and GCC will with -Wswitch-unreachable.

The previous commit should have just replaced the comment with a break
statement.

If we consider implicit fallthrough to be a design mistake of C, then
all case statements should be terminated with one of the following
statements:
* break
* continue
* return
* __attribute__(__fallthrough__)
* goto (plz no)
* (call of function with __attribute__(__noreturn__))

Fixes: 2a1390c95a69 ("nfs: Convert to use the preferred fallthrough macro")
Link: https://bugs.llvm.org/show_bug.cgi?id=47539
Suggested-by: Joe Perches <joe@...ches.com>
Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
---
Changes v2:
* add break rather than no terminating statement as per Joe.
* add Joe's suggested by tag.
* add blurb about acceptable terminal statements.

 fs/nfs/super.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/nfs/super.c b/fs/nfs/super.c
index d20326ee0475..eb2401079b04 100644
--- a/fs/nfs/super.c
+++ b/fs/nfs/super.c
@@ -889,7 +889,7 @@ static struct nfs_server *nfs_try_mount_request(struct fs_context *fc)
 		default:
 			if (rpcauth_get_gssinfo(flavor, &info) != 0)
 				continue;
-			fallthrough;
+			break;
 		}
 		dfprintk(MOUNT, "NFS: attempting to use auth flavor %u\n", flavor);
 		ctx->selected_flavor = flavor;
-- 
2.28.0.618.gf4bc123cb7-goog