linux-kernel - Re: [PATCH 3/5] asm-generic, kcsan: Add KCSAN instrumentation for bitops

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Message-ID: <20200120162725.GE2935@paulmck-ThinkPad-P72>
Date:   Mon, 20 Jan 2020 08:27:25 -0800
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Marco Elver <elver@...gle.com>, andreyknvl@...gle.com,
        glider@...gle.com, dvyukov@...gle.com, kasan-dev@...glegroups.com,
        linux-kernel@...r.kernel.org, mark.rutland@....com,
        will@...nel.org, boqun.feng@...il.com, arnd@...db.de,
        viro@...iv.linux.org.uk, christophe.leroy@....fr, dja@...ens.net,
        mpe@...erman.id.au, rostedt@...dmis.org, mhiramat@...nel.org,
        mingo@...nel.org, christian.brauner@...ntu.com,
        daniel@...earbox.net, cyphar@...har.com, keescook@...omium.org,
        linux-arch@...r.kernel.org
Subject: Re: [PATCH 3/5] asm-generic, kcsan: Add KCSAN instrumentation for
 bitops

On Mon, Jan 20, 2020 at 03:40:48PM +0100, Peter Zijlstra wrote:
> On Mon, Jan 20, 2020 at 03:19:25PM +0100, Marco Elver wrote:
> > Add explicit KCSAN checks for bitops.
> > 
> > Note that test_bit() is an atomic bitop, and we instrument it as such,
> 
> Well, it is 'atomic' in the same way that atomic_read() is. Both are
> very much not atomic ops, but are part of an interface that facilitates
> atomic operations.

True, but they all are either inline assembly or have either an
implicit or explicit cast to volatile, so they could be treated
the same as atomic_read(), correct?  If not, what am I missing?

(There is one exception, but it is in arch/x86/boot/bitops.h,
which I UP-only, correct?)

						Thanx, Paul