linux-kernel - Re: [GIT PULL] fallthrough fixes for Clang for 5.14-rc1

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Date:   Mon, 28 Jun 2021 20:12:12 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc:     Kees Cook <keescook@...omium.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [GIT PULL] fallthrough fixes for Clang for 5.14-rc1

On Mon, Jun 28, 2021 at 1:58 PM Gustavo A. R. Silva
<gustavoars@...nel.org> wrote:
>
> Please, pull the following patches that fix many fall-through warnings
> when building with Clang 12.0.0 and this[1] change reverted. Notice
> that in order to enable -Wimplicit-fallthrough for Clang, such change[1]
> is meant to be reverted at some point. So, these patches help to move
> in that direction.

I've pulled this, but I really don't like how random it is.

Just as an example - and there are many others - look at the patch to
net/netrom/nr_route.c.

It does

                case 0:
                        nr_node->routes[0] = nr_node->routes[1];
                        fallthrough;
                case 1:
                        nr_node->routes[1] = nr_node->routes[2];
+                       fallthrough;
                case 2:
                        break;

and then about a hundred lines later it does
                case 0:
                        s->routes[0] = s->routes[1];
                        fallthrough;
                case 1:
                        s->routes[1] = s->routes[2];
+                       break;
                case 2:
                        break;

Notice? One does a 'fallthrough' to the next case that does the
'break', and the other - very much equivalent case - does a 'break'.

So the whole "add 'fallthrough' or 'break'" decision doesn't seem to
have any pattern or rule at all.

                 Linus