From: Peter Zijlstra <peterz@infradead.org>
To: Marco Elver <elver@google.com>
Cc: Qian Cai <cai@lca.pw>, Will Deacon <will@kernel.org>,
Ingo Molnar <mingo@redhat.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
"paul E. McKenney" <paulmck@kernel.org>,
kasan-dev <kasan-dev@googlegroups.com>
Subject: Re: [PATCH] locking/osq_lock: fix a data race in osq_wait_next
Date: Tue, 28 Jan 2020 17:56:55 +0100 [thread overview]
Message-ID: <20200128165655.GM14914@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <CANpmjNNo6yW-y-Af7JgvWi3t==+=02hE4-pFU4OiH8yvbT3Byg@mail.gmail.com>
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.
> From what I can tell, all 'false positives' that have come up are data
> races where the consequences on the behaviour of the code is
> inconsequential. In other words, all of them would require
> understanding of the intended logic of the code, and understanding if
> the worst possible outcome of a data race changes the behaviour of the
> code in such a way that we may end up with an erroneously behaving
> system.
>
> As I have said before, KCSAN (or any data race detector) by definition
> only works at the language level. Any semantic analysis, beyond simple
> rules (such as ignore same-value stores) and annotations, is simply
> impossible since the tool can't know about the logic that the
> programmer intended.
>
> That being said, if there are simple rules (like ignore same-value
> stores) or other minimal annotations that can help reduce such 'false
> positives', more than happy to add them.
OK, so KCSAN knows about same-value-stores? If so, that ->cpu =
smp_processor_id() case really doesn't need annotation, right?
> What to do about osq_lock here? If people agree that no further
> annotations are wanted, and the reasoning above concludes there are no
> bugs, we can blacklist the file. That would, however, miss new data
> races in future.
I'm still hoping to convince you that the other case is one of those
'simple-rules' too :-)
next prev parent reply other threads:[~2020-01-28 16:57 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 [this message]
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
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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