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
next prev parent reply other threads:[~2020-01-21 16:16 UTC|newest]
Thread overview: 53+ 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 ` Marco Elver
2020-01-20 14:19 ` [PATCH 3/5] asm-generic, kcsan: Add KCSAN instrumentation for bitops Marco Elver
2020-01-20 14:19 ` 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 16:52 ` Peter Zijlstra
2020-01-20 20:23 ` Paul E. McKenney
2020-01-20 20:23 ` Paul E. McKenney
2020-01-21 9:15 ` Peter Zijlstra
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 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]
2020-01-21 16:16 ` Paul E. McKenney
2020-01-20 14:19 ` [PATCH 4/5] iov_iter: Use generic instrumented.h Marco Elver
2020-01-20 14:19 ` 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 14:25 ` 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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