From: "Paul E. McKenney" <paulmck@kernel.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Marco Elver <elver@google.com>, Qian Cai <cai@lca.pw>,
Will Deacon <will@kernel.org>, Ingo Molnar <mingo@redhat.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
kasan-dev <kasan-dev@googlegroups.com>
Subject: Re: [PATCH] locking/osq_lock: fix a data race in osq_wait_next
Date: Wed, 29 Jan 2020 11:26:02 -0800 [thread overview]
Message-ID: <20200129192602.GA2935@paulmck-ThinkPad-P72> (raw)
In-Reply-To: <20200129184935.GU14879@hirez.programming.kicks-ass.net>
On Wed, Jan 29, 2020 at 07:49:35PM +0100, Peter Zijlstra wrote:
> On Tue, Jan 28, 2020 at 04:22:53PM -0800, Paul E. McKenney wrote:
> > On Tue, Jan 28, 2020 at 05:56:55PM +0100, Peter Zijlstra wrote:
> > > On Tue, Jan 28, 2020 at 12:46:26PM +0100, Marco Elver wrote:
> > >
> > > > > Marco, any thought on improving KCSAN for this to reduce the false
> > > > > positives?
> > > >
> > > > Define 'false positive'.
> > >
> > > I'll use it where the code as written is correct while the tool
> > > complains about it.
> >
> > I could be wrong, but I would guess that Marco is looking for something
> > a little less subjective and a little more specific. ;-)
>
> How is that either? If any valid translation by a compile results in
> correct functionality, yet the tool complains, then surely we can speak
> of a objective fact.
Marco covered my concern in his point about the need to change the
compiler.
In any case, agreed, if a read does nothing but feed into the old/new
values for a CAS, the only thing a reasonable compiler (as opposed to
a just-barely-meets-the-standard demonic compiler) can do to you is to
decrease the CAS success rate.
Thanx, Paul
next prev parent reply other threads:[~2020-01-29 19:26 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-22 16:38 [PATCH] locking/osq_lock: fix a data race in osq_wait_next Qian Cai
2020-01-22 16:59 ` Will Deacon
2020-01-22 17:08 ` Qian Cai
2020-01-22 22:38 ` Marco Elver
2020-01-22 23:54 ` Qian Cai
2020-01-23 9:39 ` Peter Zijlstra
2020-01-28 3:11 ` Qian Cai
2020-01-28 11:46 ` Marco Elver
2020-01-28 12:53 ` Qian Cai
2020-01-28 16:52 ` Peter Zijlstra
2020-01-28 16:56 ` Peter Zijlstra
2020-01-29 0:22 ` Paul E. McKenney
2020-01-29 15:29 ` Marco Elver
2020-01-29 18:40 ` Peter Zijlstra
2020-01-30 13:39 ` Marco Elver
2020-01-30 13:48 ` Peter Zijlstra
2020-01-31 3:32 ` Qian Cai
2020-01-29 18:49 ` Peter Zijlstra
2020-01-29 19:26 ` Paul E. McKenney [this message]
2020-01-23 9:36 ` Peter Zijlstra
2020-01-28 3:12 ` Qian Cai
2020-01-28 8:18 ` Marco Elver
2020-01-28 10:10 ` Qian Cai
2020-01-28 10:29 ` Marco Elver
2020-01-22 17:09 ` Peter Zijlstra
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