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From: "Paul E. McKenney" <paulmck@kernel.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Marco Elver <elver@google.com>,
	andreyknvl@google.com, glider@google.com, dvyukov@google.com,
	kasan-dev@googlegroups.com, linux-kernel@vger.kernel.org,
	mark.rutland@arm.com, will@kernel.org, boqun.feng@gmail.com,
	arnd@arndb.de, viro@zeniv.linux.org.uk, christophe.leroy@c-s.fr,
	dja@axtens.net, mpe@ellerman.id.au, rostedt@goodmis.org,
	mhiramat@kernel.org, mingo@kernel.org,
	christian.brauner@ubuntu.com, daniel@iogearbox.net,
	cyphar@cyphar.com, keescook@chromium.org,
	linux-arch@vger.kernel.org
Subject: Re: [PATCH 3/5] asm-generic, kcsan: Add KCSAN instrumentation for bitops
Date: Tue, 21 Jan 2020 08:16:32 -0800	[thread overview]
Message-ID: <20200121161632.GV2935@paulmck-ThinkPad-P72> (raw)
In-Reply-To: <20200121144716.GQ14879@hirez.programming.kicks-ass.net>

On Tue, Jan 21, 2020 at 03:47:16PM +0100, Peter Zijlstra wrote:
> On Tue, Jan 21, 2020 at 06:21:09AM -0800, Paul E. McKenney wrote:
> > On Tue, Jan 21, 2020 at 10:15:01AM +0100, Peter Zijlstra wrote:
> > > On Mon, Jan 20, 2020 at 12:23:59PM -0800, Paul E. McKenney wrote:
> > > > We also don't have __atomic_read() and __atomic_set(), yet atomic_read()
> > > > and atomic_set() are considered to be non-racy, right?
> > > 
> > > What is racy? :-) You can make data races with atomic_{read,set}() just
> > > fine.
> > 
> > Like "fairness", lots of definitions of "racy".  ;-)
> > 
> > > Anyway, traditionally we call the read-modify-write stuff atomic, not
> > > the trivial load-store stuff. The only reason we care about the
> > > load-store stuff in the first place is because C compilers are shit.
> > > 
> > > atomic_read() / test_bit() are just a load, all we need is the C
> > > compiler not to be an ass and split it. Yes, we've invented the term
> > > single-copy atomicity for that, but that doesn't make it more or less of
> > > a load.
> > > 
> > > And exactly because it is just a load, there is no __test_bit(), which
> > > would be the exact same load.
> > 
> > Very good!  Shouldn't KCSAN then define test_bit() as non-racy just as
> > for atomic_read()?
> 
> Sure it does; but my comment was aimed at the gripe that test_bit()
> lives in the non-atomic bitops header. That is arguably entirely
> correct.

Fair enough!

							Thanx, Paul

  parent reply	other threads:[~2020-01-21 16:16 UTC|newest]

Thread overview: 44+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-20 14:19 [PATCH 1/5] include/linux: Add instrumented.h infrastructure Marco Elver
2020-01-20 14:19 ` [PATCH 2/5] asm-generic, atomic-instrumented: Use generic instrumented.h Marco Elver
2020-01-20 14:19 ` [PATCH 3/5] asm-generic, kcsan: Add KCSAN instrumentation for bitops Marco Elver
2020-01-20 14:40   ` Peter Zijlstra
2020-01-20 16:27     ` Paul E. McKenney
2020-01-20 16:52       ` Peter Zijlstra
2020-01-20 20:23         ` Paul E. McKenney
2020-01-21  9:15           ` Peter Zijlstra
2020-01-21 14:21             ` Paul E. McKenney
2020-01-21 14:47               ` Peter Zijlstra
2020-01-21 15:07                 ` Marco Elver
2020-01-21 15:07                   ` Marco Elver
2020-01-21 16:16                 ` Paul E. McKenney [this message]
2020-01-20 14:19 ` [PATCH 4/5] iov_iter: Use generic instrumented.h Marco Elver
2020-01-20 14:19 ` [PATCH 5/5] copy_to_user, copy_from_user: " Marco Elver
2020-01-20 14:51   ` Dmitry Vyukov
2020-01-20 14:51     ` Dmitry Vyukov
2020-01-20 15:05     ` Marco Elver
2020-01-20 15:05       ` Marco Elver
2020-01-20 14:25 ` [PATCH 1/5] include/linux: Add instrumented.h infrastructure Alexander Potapenko
2020-01-20 14:34 ` Dmitry Vyukov
2020-01-20 14:34   ` Dmitry Vyukov
2020-01-20 15:53   ` Marco Elver
2020-01-20 15:53     ` Marco Elver
2020-01-20 14:45 ` Dmitry Vyukov
2020-01-20 14:45   ` Dmitry Vyukov
2020-01-20 14:58   ` Dmitry Vyukov
2020-01-20 14:58     ` Dmitry Vyukov
2020-01-20 15:09     ` Dmitry Vyukov
2020-01-20 15:09       ` Dmitry Vyukov
2020-01-20 15:40       ` Marco Elver
2020-01-20 15:40         ` Marco Elver
2020-01-20 16:06         ` Dmitry Vyukov
2020-01-20 16:06           ` Dmitry Vyukov
2020-01-20 16:25           ` Marco Elver
2020-01-20 16:25             ` Marco Elver
2020-01-20 16:39             ` Dmitry Vyukov
2020-01-20 16:39               ` Dmitry Vyukov
2020-01-21  9:44               ` Marco Elver
2020-01-21  9:44                 ` Marco Elver
2020-01-21 13:01   ` Dmitry Vyukov
2020-01-21 13:01     ` Dmitry Vyukov
2020-01-21 16:14     ` Marco Elver
2020-01-21 16:14       ` Marco Elver

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