linux-kernel - Re: [PATCH -rcu/kcsan 05/23] kcsan: Add core memory barrier instrumentation functions

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Message-ID: <YVw63tqctCMm+d7M@hirez.programming.kicks-ass.net>
Date:   Tue, 5 Oct 2021 13:45:34 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Marco Elver <elver@...gle.com>
Cc:     "Paul E . McKenney" <paulmck@...nel.org>,
        Alexander Potapenko <glider@...gle.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Borislav Petkov <bp@...en8.de>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Ingo Molnar <mingo@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Waiman Long <longman@...hat.com>,
        Will Deacon <will@...nel.org>, kasan-dev@...glegroups.com,
        linux-arch@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, x86@...nel.org
Subject: Re: [PATCH -rcu/kcsan 05/23] kcsan: Add core memory barrier
 instrumentation functions

On Tue, Oct 05, 2021 at 01:41:18PM +0200, Peter Zijlstra wrote:
> On Tue, Oct 05, 2021 at 12:58:47PM +0200, Marco Elver wrote:
> > +static __always_inline void kcsan_atomic_release(int memorder)
> > +{
> > +	if (memorder == __ATOMIC_RELEASE ||
> > +	    memorder == __ATOMIC_SEQ_CST ||
> > +	    memorder == __ATOMIC_ACQ_REL)
> > +		__kcsan_release();
> > +}
> > +
> >  #define DEFINE_TSAN_ATOMIC_LOAD_STORE(bits)                                                        \
> >  	u##bits __tsan_atomic##bits##_load(const u##bits *ptr, int memorder);                      \
> >  	u##bits __tsan_atomic##bits##_load(const u##bits *ptr, int memorder)                       \
> >  	{                                                                                          \
> > +		kcsan_atomic_release(memorder);                                                    \
> >  		if (!IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS)) {                                    \
> >  			check_access(ptr, bits / BITS_PER_BYTE, KCSAN_ACCESS_ATOMIC, _RET_IP_);    \
> >  		}                                                                                  \
> > @@ -1156,6 +1187,7 @@ EXPORT_SYMBOL(__tsan_init);
> >  	void __tsan_atomic##bits##_store(u##bits *ptr, u##bits v, int memorder);                   \
> >  	void __tsan_atomic##bits##_store(u##bits *ptr, u##bits v, int memorder)                    \
> >  	{                                                                                          \
> > +		kcsan_atomic_release(memorder);                                                    \
> >  		if (!IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS)) {                                    \
> >  			check_access(ptr, bits / BITS_PER_BYTE,                                    \
> >  				     KCSAN_ACCESS_WRITE | KCSAN_ACCESS_ATOMIC, _RET_IP_);          \
> > @@ -1168,6 +1200,7 @@ EXPORT_SYMBOL(__tsan_init);
> >  	u##bits __tsan_atomic##bits##_##op(u##bits *ptr, u##bits v, int memorder);                 \
> >  	u##bits __tsan_atomic##bits##_##op(u##bits *ptr, u##bits v, int memorder)                  \
> >  	{                                                                                          \
> > +		kcsan_atomic_release(memorder);                                                    \
> >  		if (!IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS)) {                                    \
> >  			check_access(ptr, bits / BITS_PER_BYTE,                                    \
> >  				     KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_WRITE |                  \
> > @@ -1200,6 +1233,7 @@ EXPORT_SYMBOL(__tsan_init);
> >  	int __tsan_atomic##bits##_compare_exchange_##strength(u##bits *ptr, u##bits *exp,          \
> >  							      u##bits val, int mo, int fail_mo)    \
> >  	{                                                                                          \
> > +		kcsan_atomic_release(mo);                                                          \
> >  		if (!IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS)) {                                    \
> >  			check_access(ptr, bits / BITS_PER_BYTE,                                    \
> >  				     KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_WRITE |                  \
> > @@ -1215,6 +1249,7 @@ EXPORT_SYMBOL(__tsan_init);
> >  	u##bits __tsan_atomic##bits##_compare_exchange_val(u##bits *ptr, u##bits exp, u##bits val, \
> >  							   int mo, int fail_mo)                    \
> >  	{                                                                                          \
> > +		kcsan_atomic_release(mo);                                                          \
> >  		if (!IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS)) {                                    \
> >  			check_access(ptr, bits / BITS_PER_BYTE,                                    \
> >  				     KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_WRITE |                  \
> > @@ -1246,6 +1281,7 @@ DEFINE_TSAN_ATOMIC_OPS(64);
> >  void __tsan_atomic_thread_fence(int memorder);
> >  void __tsan_atomic_thread_fence(int memorder)
> >  {
> > +	kcsan_atomic_release(memorder);
> >  	__atomic_thread_fence(memorder);
> >  }
> >  EXPORT_SYMBOL(__tsan_atomic_thread_fence);
> 
> I find that very hard to read.. kcsan_atomic_release() it not in fact a
> release. It might be a release if @memorder implies one.

Also, what's the atomic part signify? Is that because you're modeling
the difference in acquire/release semantics between
smp_load_{acquire,release}() and atomic*_{acquire,release}() ?