From: "Luck, Tony" <tony.luck@intel.com>
To: Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
"Lobakin, Alexandr" <alexandr.lobakin@intel.com>
Cc: 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>,
Marco Elver <elver@google.com>, 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.>
Subject: RE: [PATCH v2 2/6] bitops: always define asm-generic non-atomic bitops
Date: Fri, 10 Jun 2022 16:02:03 +0000 [thread overview]
Message-ID: <22042c14bc6a437d9c6b235fbfa32c8a@intel.com> (raw)
In-Reply-To: <YqNMO0ioGzJ1IkoA@smile.fi.intel.com>
> > +/**
> > + * generic_test_bit - Determine whether a bit is set
> > + * @nr: bit number to test
> > + * @addr: Address to start counting from
> > + */
>
> Shouldn't we add in this or in separate patch a big NOTE to explain that this
> is actually atomic and must be kept as a such?
"atomic" isn't really the right word. The volatile access makes sure that the
compiler does the test at the point that the source code asked, and doesn't
move it before/after other operations.
But there is no such thing as an atomic test_bit() operation:
if (test_bit(5, addr)) {
/* some other CPU nukes bit 5 */
/* I know it was set when I looked, but now, could be anything */
...
}
-Tony
WARNING: multiple messages have this Message-ID (diff)
From: "Luck, Tony" <tony.luck@intel.com>
To: Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
"Lobakin, Alexandr" <alexandr.lobakin@intel.com>
Cc: 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>,
Marco Elver <elver@google.com>, 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
Date: Fri, 10 Jun 2022 16:02:03 +0000 [thread overview]
Message-ID: <22042c14bc6a437d9c6b235fbfa32c8a@intel.com> (raw)
In-Reply-To: <YqNMO0ioGzJ1IkoA@smile.fi.intel.com>
> > +/**
> > + * generic_test_bit - Determine whether a bit is set
> > + * @nr: bit number to test
> > + * @addr: Address to start counting from
> > + */
>
> Shouldn't we add in this or in separate patch a big NOTE to explain that this
> is actually atomic and must be kept as a such?
"atomic" isn't really the right word. The volatile access makes sure that the
compiler does the test at the point that the source code asked, and doesn't
move it before/after other operations.
But there is no such thing as an atomic test_bit() operation:
if (test_bit(5, addr)) {
/* some other CPU nukes bit 5 */
/* I know it was set when I looked, but now, could be anything */
...
}
-Tony
next prev parent reply other threads:[~2022-06-10 16:02 UTC|newest]
Thread overview: 85+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-10 11:34 [PATCH v2 0/6] bitops: let optimize out non-atomic bitops on compile-time constants Alexander Lobakin
2022-06-10 11:34 ` Alexander Lobakin
2022-06-10 11:34 ` Alexander Lobakin
2022-06-10 11:34 ` [PATCH v2 1/6] ia64, processor: fix -Wincompatible-pointer-types in ia64_get_irr() Alexander Lobakin
2022-06-10 11:34 ` Alexander Lobakin
2022-06-10 11:34 ` Alexander Lobakin
2022-06-10 12:18 ` David Laight
2022-06-10 12:18 ` David Laight
2022-06-10 13:46 ` Andy Shevchenko
2022-06-10 13:46 ` Andy Shevchenko
2022-06-10 13:46 ` Andy Shevchenko
2022-06-15 2:59 ` Yury Norov
2022-06-15 2:59 ` Yury Norov
2022-06-15 2:59 ` Yury Norov
2022-06-10 11:34 ` [PATCH v2 2/6] bitops: always define asm-generic non-atomic bitops Alexander Lobakin
2022-06-10 11:34 ` Alexander Lobakin
2022-06-10 11:34 ` Alexander Lobakin
2022-06-10 13:50 ` Andy Shevchenko
2022-06-10 13:50 ` Andy Shevchenko
2022-06-10 13:50 ` Andy Shevchenko
2022-06-10 16:02 ` Luck, Tony [this message]
2022-06-10 16:02 ` Luck, Tony
2022-06-10 16:32 ` Marco Elver
2022-06-10 16:32 ` Marco Elver
2022-06-10 16:32 ` Marco Elver
2022-06-13 14:19 ` Alexander Lobakin
2022-06-13 14:19 ` Alexander Lobakin
2022-06-13 14:19 ` Alexander Lobakin
2022-06-13 14:33 ` Marco Elver
2022-06-13 14:33 ` Marco Elver
2022-06-13 14:33 ` Marco Elver
2022-06-15 2:47 ` Yury Norov
2022-06-15 2:47 ` Yury Norov
2022-06-15 2:47 ` Yury Norov
2022-06-15 7:46 ` Marco Elver
2022-06-15 7:46 ` Marco Elver
2022-06-15 7:46 ` Marco Elver
2022-06-13 16:26 ` Luck, Tony
2022-06-13 16:26 ` Luck, Tony
2022-06-13 21:29 ` David Laight
2022-06-13 21:29 ` David Laight
2022-06-10 11:34 ` [PATCH v2 3/6] bitops: unify non-atomic bitops prototypes across architectures Alexander Lobakin
2022-06-10 11:34 ` Alexander Lobakin
2022-06-10 11:34 ` Alexander Lobakin
2022-06-10 11:34 ` [PATCH v2 4/6] bitops: define const_*() versions of the non-atomics Alexander Lobakin
2022-06-10 11:34 ` Alexander Lobakin
2022-06-10 11:34 ` Alexander Lobakin
2022-06-10 13:56 ` Andy Shevchenko
2022-06-10 13:56 ` Andy Shevchenko
2022-06-10 13:56 ` Andy Shevchenko
2022-06-13 14:30 ` Alexander Lobakin
2022-06-13 14:30 ` Alexander Lobakin
2022-06-13 14:30 ` Alexander Lobakin
2022-06-15 2:57 ` Yury Norov
2022-06-15 2:57 ` Yury Norov
2022-06-15 2:57 ` Yury Norov
2022-06-15 13:55 ` Alexander Lobakin
2022-06-15 13:55 ` Alexander Lobakin
2022-06-15 13:55 ` Alexander Lobakin
2022-06-15 15:52 ` David Laight
2022-06-15 15:52 ` David Laight
2022-06-10 11:34 ` [PATCH v2 5/6] bitops: wrap non-atomic bitops with a transparent macro Alexander Lobakin
2022-06-10 11:34 ` Alexander Lobakin
2022-06-10 11:34 ` Alexander Lobakin
2022-06-10 11:34 ` [PATCH v2 6/6] bitops: let optimize out non-atomic bitops on compile-time constants Alexander Lobakin
2022-06-10 11:34 ` Alexander Lobakin
2022-06-10 11:34 ` Alexander Lobakin
2022-06-15 3:26 ` Yury Norov
2022-06-15 3:26 ` Yury Norov
2022-06-15 3:26 ` Yury Norov
2022-06-15 14:00 ` Alexander Lobakin
2022-06-15 14:00 ` Alexander Lobakin
2022-06-15 14:00 ` Alexander Lobakin
2022-06-13 7:35 ` [PATCH v2 0/6] " Geert Uytterhoeven
2022-06-13 7:35 ` Geert Uytterhoeven
2022-06-13 7:35 ` Geert Uytterhoeven
2022-06-13 14:26 ` Alexander Lobakin
2022-06-13 14:26 ` Alexander Lobakin
2022-06-13 14:26 ` Alexander Lobakin
2022-06-13 15:22 ` Geert Uytterhoeven
2022-06-13 15:22 ` Geert Uytterhoeven
2022-06-13 15:22 ` Geert Uytterhoeven
2022-06-15 14:17 ` Alexander Lobakin
2022-06-15 14:17 ` Alexander Lobakin
2022-06-15 14:17 ` Alexander Lobakin
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