Re: [chrome-os:chromeos-4.19 21350/21402] drivers/misc/echo/echo.c:384:27: error: equality comparison with extraneous parentheses

From: Nathan Chancellor <natechancellor@gmail.com>
To: Sasha Levin <sashal@kernel.org>
Cc: Nick Desaulniers <ndesaulniers@google.com>,
	Greg KH <gregkh@linuxfoundation.org>,
	"# 3.4.x" <stable@vger.kernel.org>,
	Guenter Roeck <groeck@google.com>,
	kbuild test robot <lkp@intel.com>,
	cros-kernel-buildreports@googlegroups.com,
	kbuild-all@lists.01.org,
	clang-built-linux <clang-built-linux@googlegroups.com>
Subject: Re: [chrome-os:chromeos-4.19 21350/21402] drivers/misc/echo/echo.c:384:27: error: equality comparison with extraneous parentheses
Date: Wed, 15 Apr 2020 20:39:22 -0700	[thread overview]
Message-ID: <20200416033922.GA19745@ubuntu-s3-xlarge-x86> (raw)
In-Reply-To: <20200416033100.GH1068@sasha-vm>

On Wed, Apr 15, 2020 at 11:31:00PM -0400, Sasha Levin wrote:
> On Wed, Apr 15, 2020 at 10:51:37AM -0700, Nick Desaulniers wrote:
> > On Tue, Apr 14, 2020 at 5:56 PM 'Guenter Roeck' via Clang Built Linux
> > <clang-built-linux@googlegroups.com> wrote:
> > > 
> > > On Tue, Apr 14, 2020 at 5:26 PM Nathan Chancellor
> > > <natechancellor@gmail.com> wrote:
> > > >
> > > > Hi all,
> > > >
> > > > Sorry for yet another convergeance on this commit... :/ hopefully this
> > > > does not continue for much longer. None of the warnings are obviously
> > > > caused by the patch below.
> > > > Fixed by commit 85dc2c65e6c9 ("misc: echo: Remove unnecessary
> > > > parentheses and simplify check for zero").
> > > >
> > > No worries.
> > > 
> > > I noticed that the problems are pretty much all fixed in the upstream
> > > kernel. I just wasn't sure if it would be worthwhile sending a request
> > > to stable@ to have them applied to 4.19.y (and if necessary 5.4.y).
> > > Any suggestions ?
> > 
> > We should strive to be warning free on stable.  Thanks for identifying
> > the fix Nathan.
> > 
> > Greg, Sasha,
> > Would you please cherry pick 85dc2c65e6c9 to 4.19.y, 4.14.y, 4.9.y,
> > and 4.4.y (maybe 3.18, didn't check that one)? It applies cleanly and
> > is a trivial fix for a warning that landed in v4.20-rc1.
> 
> I'll grab it, but could we please look into disabling some clang
> warnings?
> 
> I understand warnings that might warn us about dangerous code, but this
> reads to me like something checkpatch might complain about...
> 
> -- 
> Thanks,
> Sasha

For what it's worth, I have fixed all of these (at least that I know of)
in mainline so there is no point in disabling it there. If you want to
disable it in stable, that's a different discussion. Another option
would be asking the 0day team not to run randconfig builds with clang on
stable trees. I'd prefer that over disabling the warning.

This warning wants to make sure that (a == b) and ((a = b)) do not get
mixed up, which seems worthwhile: https://godbolt.org/z/GUdL5X

Cheers,
Nathan