From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Luck, Tony" <tony.luck@intel.com>
Subject: RE: [PATCH v2 2/6] bitops: always define asm-generic non-atomic
 bitops
Date: Mon, 13 Jun 2022 16:26:49 +0000
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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-m6

>> 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