From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Marco Elver <elver@google.com>, Will Deacon <will@kernel.org>,
paulmck <paulmck@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Segher Boessenkool <segher@kernel.crashing.org>,
linux-kernel <linux-kernel@vger.kernel.org>,
Alan Stern <stern@rowland.harvard.edu>,
Andrea Parri <parri.andrea@gmail.com>,
Boqun Feng <boqun.feng@gmail.com>,
Nicholas Piggin <npiggin@gmail.com>,
David Howells <dhowells@redhat.com>,
j alglave <j.alglave@ucl.ac.uk>,
luc maranget <luc.maranget@inria.fr>, akiyks <akiyks@gmail.com>,
linux-toolchains <linux-toolchains@vger.kernel.org>,
linux-arch <linux-arch@vger.kernel.org>
Subject: Re: [RFC PATCH] LKMM: Add ctrl_dep() macro for control dependency
Date: Fri, 1 Oct 2021 13:28:01 -0400 (EDT) [thread overview]
Message-ID: <1097444747.48074.1633109281556.JavaMail.zimbra@efficios.com> (raw)
In-Reply-To: <CAHk-=whcN4ACLFvst0THwwpUFK4DDSM4O_frSoUQJ1m+0ENWjw@mail.gmail.com>
----- On Oct 1, 2021, at 12:20 PM, Linus Torvalds torvalds@linux-foundation.org wrote:
[...]
> But again - a lot of these made-up examples are exactly that: made up.
> For us to have a ctrl_dep() macro, I really want to see an actual
> honest-to-goodness case of this that we can point to.
I've spent some quality time staring at generated assembler diff in the past
days, and looking for code patterns of refcount_dec_and_test users, without
much success. There are some cases which end up working by chance, e.g. in
cases where the if leg has a smp_acquire__after_ctrl_dep and the else leg has
code that emits a barrier(), but I did not find any buggy generated
code per se. In order to observe those issues in real life, we would
really need to have identical then/else legs to the branch.
Thanks,
Mathieu
--
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com
next prev parent reply other threads:[~2021-10-01 17:28 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-28 21:15 [RFC PATCH] LKMM: Add ctrl_dep() macro for control dependency Mathieu Desnoyers
2021-09-29 12:06 ` Marco Elver
2021-10-01 15:45 ` Mathieu Desnoyers
2021-10-01 16:20 ` Linus Torvalds
2021-10-01 17:28 ` Mathieu Desnoyers [this message]
2021-10-01 18:18 ` Linus Torvalds
2021-09-29 12:28 ` Florian Weimer
2021-09-29 17:41 ` Segher Boessenkool
2021-09-29 19:46 ` Florian Weimer
2021-10-01 16:13 ` Mathieu Desnoyers
2021-10-01 16:26 ` Florian Weimer
2021-10-01 16:35 ` Linus Torvalds
2021-10-10 14:02 ` Florian Weimer
2021-10-14 0:01 ` Paul E. McKenney
2021-10-14 2:14 ` Alan Stern
2021-10-14 16:14 ` Paul E. McKenney
2021-10-14 15:58 ` Florian Weimer
2021-10-14 16:23 ` Paul E. McKenney
2021-10-14 18:19 ` Florian Weimer
2021-10-14 21:09 ` Paul E. McKenney
2021-10-14 22:36 ` Linus Torvalds
2021-09-30 13:28 ` Mathieu Desnoyers
2021-09-29 14:47 ` Linus Torvalds
2021-09-29 14:54 ` Linus Torvalds
2021-09-29 19:50 ` Mathieu Desnoyers
2021-09-29 20:13 ` Mathieu Desnoyers
2021-09-29 19:27 ` Mathieu Desnoyers
2021-09-29 22:14 ` Linus Torvalds
2021-09-29 21:47 ` Segher Boessenkool
2021-09-29 23:57 ` Paul E. McKenney
2021-10-01 15:28 ` Mathieu Desnoyers
2021-10-01 22:53 ` Paul E. McKenney
2021-10-01 19:10 ` Segher Boessenkool
2021-10-01 22:50 ` Paul E. McKenney
2021-10-02 14:29 ` Alan Stern
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