linux-kernel - Re: [PATCH 05/10] ide: Remove uninitialized

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Message-ID: <CAKwvOdk3Wc1gC0UMsFZsZqQ8n_bkPjNAJo5u3nfcyXcBaZCMHw@mail.gmail.com>
Date:   Thu, 4 Jun 2020 13:29:44 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
        Alexander Potapenko <glider@...gle.com>,
        Joe Perches <joe@...ches.com>,
        Andy Whitcroft <apw@...onical.com>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        drbd-dev@...ts.linbit.com, linux-block@...r.kernel.org,
        b43-dev@...ts.infradead.org,
        Network Development <netdev@...r.kernel.org>,
        linux-wireless <linux-wireless@...r.kernel.org>,
        linux-ide@...r.kernel.org, linux-clk@...r.kernel.org,
        linux-spi@...r.kernel.org,
        Linux Memory Management List <linux-mm@...ck.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Saravana Kannan <saravanak@...gle.com>
Subject: Re: [PATCH 05/10] ide: Remove uninitialized_var() usage

On Thu, Jun 4, 2020 at 1:20 PM Kees Cook <keescook@...omium.org> wrote:
>
> On Thu, Jun 04, 2020 at 12:29:17PM -0700, Nick Desaulniers wrote:
> > On Wed, Jun 3, 2020 at 4:32 PM Kees Cook <keescook@...omium.org> wrote:
> > >
> > > Using uninitialized_var() is dangerous as it papers over real bugs[1]
> > > (or can in the future), and suppresses unrelated compiler warnings (e.g.
> > > "unused variable"). If the compiler thinks it is uninitialized, either
> > > simply initialize the variable or make compiler changes. As a precursor
> > > to removing[2] this[3] macro[4], just remove this variable since it was
> > > actually unused:
> > >
> > > drivers/ide/ide-taskfile.c:232:34: warning: unused variable 'flags' [-Wunused-variable]
> > >         unsigned long uninitialized_var(flags);
> > >                                         ^
> > >
> > > [1] https://lore.kernel.org/lkml/20200603174714.192027-1-glider@google.com/
> > > [2] https://lore.kernel.org/lkml/CA+55aFw+Vbj0i=1TGqCR5vQkCzWJ0QxK6CernOU6eedsudAixw@mail.gmail.com/
> > > [3] https://lore.kernel.org/lkml/CA+55aFwgbgqhbp1fkxvRKEpzyR5J8n1vKT1VZdz9knmPuXhOeg@mail.gmail.com/
> > > [4] https://lore.kernel.org/lkml/CA+55aFz2500WfbKXAx8s67wrm9=yVJu65TpLgN_ybYNv0VEOKA@mail.gmail.com/
> > >
> > > Signed-off-by: Kees Cook <keescook@...omium.org>
> >
> > Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>
>
> Thanks for the reviews!
>
> > Fixes ce1e518190ea ("ide: don't disable interrupts during kmap_atomic()")
>
> I originally avoided adding Fixes tags because I didn't want these
> changes backported into a -stable without -Wmaybe-uninitialized
> disabled, but in these cases (variable removal), that actually does make
> sense. Thanks!

Saravana showed me a cool trick for quickly finding commits that
removed a particular identifier that I find faster than `git blame` or
vim-fugitive for the purpose of Fixes tags:
$ git log -S <string> <file>
I've added it to our wiki:
https://github.com/ClangBuiltLinux/linux/wiki/Command-line-tips-and-tricks#for-finding-which-commit-may-have-removed-a-string-try.
I should update the first tip; what was your suggestion for
constraining the search to the current remote?
-- 
Thanks,
~Nick Desaulniers