Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
From:   "Luck, Tony" <tony.luck@intel.com>
To:     "Lobakin, Alexandr" <alexandr.lobakin@intel.com>,
        Marco Elver <elver@google.com>
CC:     Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Arnd Bergmann <arnd@arndb.de>,
        Yury Norov <yury.norov@gmail.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Matt Turner <mattst88@gmail.com>,
        Brian Cain <bcain@quicinc.com>,
        Geert Uytterhoeven <geert@linux-m68k.org>,
        "Yoshinori Sato" <ysato@users.sourceforge.jp>,
        Rich Felker <dalias@libc.org>,
        "David S. Miller" <davem@davemloft.net>,
        Kees Cook <keescook@chromium.org>,
        "Peter Zijlstra (Intel)" <peterz@infradead.org>,
        Borislav Petkov <bp@suse.de>,
        "Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
        "linux-alpha@vger.kernel.org" <linux-alpha@vger.kernel.org>,
        "linux-hexagon@vger.kernel.org" <linux-hexagon@vger.kernel.org>,
        "linux-ia64@vger.kernel.org" <linux-ia64@vger.kernel.org>,
        "linux-m68k@lists.linux-m68k.org" <linux-m68k@lists.linux-m68k.org>,
        "linux-sh@vger.kernel.org" <linux-sh@vger.kernel.org>,
        "sparclinux@vger.kernel.org" <sparclinux@vger.kernel.org>,
        "linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH v2 2/6] bitops: always define asm-generic non-atomic
 bitops
Thread-Topic: [PATCH v2 2/6] bitops: always define asm-generic non-atomic
 bitops
Thread-Index: AQHYfL4xWJEoq3eTcEeKREBjFjjrHK1JHg2A//+t5kCAAH9LAIAEkeOA//+tDzA=
Date:   Mon, 13 Jun 2022 16:26:49 +0000
Message-ID: <c82877aa7cc244f2bf0f65dfb2b617e7@intel.com>
References: <20220610113427.908751-1-alexandr.lobakin@intel.com>
 <20220610113427.908751-3-alexandr.lobakin@intel.com>
 <YqNMO0ioGzJ1IkoA@smile.fi.intel.com>
 <22042c14bc6a437d9c6b235fbfa32c8a@intel.com>
 <CANpmjNNZAeMQjzNyXLeKY4cp_m-xJBU1vs7PgT+7_sJwxtEEAg@mail.gmail.com>
 <20220613141947.1176100-1-alexandr.lobakin@intel.com>
In-Reply-To: <20220613141947.1176100-1-alexandr.lobakin@intel.com>
Accept-Language: en-US
Content-Language: en-US
dlp-product: dlpe-windows
dlp-reaction: no-action
dlp-version: 11.6.500.17
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: quoted-printable
MIME-Version: 1.0
Precedence: bulk

>> It's listed in Documentation/atomic_bitops.txt.
>
> Oh, so my memory was actually correct that I saw it in the docs
> somewhere.
> WDYT, should I mention this here in the code (block comment) as well
> that it's atomic and must not lose `volatile` as Andy suggested or
> it's sufficient to have it in the docs (+ it's not underscored)?

I think a comment that the "volatile" is required to prevent re-ordering
is enough.

But maybe others are sufficiently clear on the meaning? I once wasted
time looking for the non-atomic __test_bit() version (to use in some code
that was already protected by a spin lock, so didn't need the overhead
of an "atomic" version) before realizing there wasn't a non-atomic one.

-Tony