From: Linus Torvalds <torvalds@linux-foundation.org>
To: Jonas Oberhauser <jonas.oberhauser@huaweicloud.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Boqun Feng <boqun.feng@gmail.com>,
linux-kernel@vger.kernel.org, rcu@vger.kernel.org,
linux-mm@kvack.org, lkmm@lists.linux.dev,
"Paul E. McKenney" <paulmck@kernel.org>,
Frederic Weisbecker <frederic@kernel.org>,
Neeraj Upadhyay <neeraj.upadhyay@kernel.org>,
Joel Fernandes <joel@joelfernandes.org>,
Josh Triplett <josh@joshtriplett.org>,
"Uladzislau Rezki (Sony)" <urezki@gmail.com>,
rostedt <rostedt@goodmis.org>,
Lai Jiangshan <jiangshanlai@gmail.com>,
Zqiang <qiang.zhang1211@gmail.com>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>, Will Deacon <will@kernel.org>,
Waiman Long <longman@redhat.com>,
Mark Rutland <mark.rutland@arm.com>,
Thomas Gleixner <tglx@linutronix.de>,
Kent Overstreet <kent.overstreet@gmail.com>,
Vlastimil Babka <vbabka@suse.cz>,
maged.michael@gmail.com,
Neeraj Upadhyay <neeraj.upadhyay@amd.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Subject: Re: [RFC PATCH 1/4] hazptr: Add initial implementation of hazard pointers
Date: Fri, 27 Sep 2024 13:24:07 -0700 [thread overview]
Message-ID: <CAHk-=whteT=CDW09TMk4wwwYs+qvcAKQUfw8+1D-e8H4XhFs3A@mail.gmail.com> (raw)
In-Reply-To: <CAHk-=wgi9vqh6qUpPKSydfdqd3210MnekZ1VxB6aAmfqz2bFpw@mail.gmail.com>
On Fri, 27 Sept 2024 at 12:28, Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> Dammit, people, read the code I posted.
Actually, no, apologies. You were right, and I was wrong.
It does need both of the sources of the comparison to be hidden,
because while even hiding just one side makes the comparison result
"meaningless" as far as the compiler is concerned, the compiler will
still have generated a pseudo for the hidden value, and might decide
that it can re-use that pseudo for the non-hidden pointer if the two
then match.
So yeah, the example function I posted should be safe, but my "you can
probably make do with hiding just one side" was actually a bogus and
invalid optimization. You do need to hide both sides. Not just for
clarity, but for correctness.
Linus
next prev parent reply other threads:[~2024-09-27 20:24 UTC|newest]
Thread overview: 66+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-09-17 14:33 [RFC PATCH 0/4] Add hazard pointers to kernel Boqun Feng
2024-09-17 14:33 ` [RFC PATCH 1/4] hazptr: Add initial implementation of hazard pointers Boqun Feng
2024-09-18 8:27 ` Mathieu Desnoyers
2024-09-18 15:17 ` Alan Huang
2024-09-19 6:56 ` Boqun Feng
2024-09-19 18:07 ` Jonas Oberhauser
2024-09-19 0:12 ` Jann Horn
2024-09-19 20:30 ` Jonas Oberhauser
2024-09-20 7:43 ` Jonas Oberhauser
2024-09-19 6:39 ` Lai Jiangshan
2024-09-19 7:10 ` Boqun Feng
2024-09-19 12:33 ` Alan Huang
2024-09-19 13:57 ` Alan Huang
2024-09-19 18:58 ` Boqun Feng
2024-09-19 19:53 ` Alan Huang
2024-09-19 16:10 ` Alan Huang
2024-09-19 14:00 ` Jonas Oberhauser
2024-09-20 7:41 ` Jonas Oberhauser
2024-09-25 10:02 ` Boqun Feng
2024-09-25 10:11 ` Jonas Oberhauser
2024-09-25 10:45 ` Boqun Feng
2024-09-25 11:59 ` Mathieu Desnoyers
2024-09-25 12:16 ` Boqun Feng
2024-09-25 12:47 ` Mathieu Desnoyers
2024-09-25 13:10 ` Mathieu Desnoyers
2024-09-25 13:20 ` Mathieu Desnoyers
2024-09-26 6:16 ` Mathieu Desnoyers
2024-09-26 15:53 ` Jonas Oberhauser
2024-09-26 16:12 ` Linus Torvalds
2024-09-26 16:40 ` Jonas Oberhauser
2024-09-26 16:54 ` Linus Torvalds
2024-09-27 0:01 ` Boqun Feng
2024-09-27 1:30 ` Mathieu Desnoyers
2024-09-27 1:37 ` Boqun Feng
2024-09-27 4:28 ` Boqun Feng
2024-09-27 10:59 ` Mathieu Desnoyers
2024-09-27 14:43 ` Mathieu Desnoyers
2024-09-27 15:22 ` Mathieu Desnoyers
2024-09-27 16:06 ` Alan Huang
2024-09-27 16:44 ` Linus Torvalds
2024-09-27 17:15 ` Mathieu Desnoyers
2024-09-27 17:23 ` Linus Torvalds
2024-09-27 17:51 ` Mathieu Desnoyers
2024-09-27 18:13 ` Linus Torvalds
2024-09-27 19:12 ` Jonas Oberhauser
2024-09-27 19:28 ` Linus Torvalds
2024-09-27 20:24 ` Linus Torvalds [this message]
2024-09-27 20:02 ` Mathieu Desnoyers
2024-09-27 1:20 ` Mathieu Desnoyers
2024-09-27 4:38 ` Boqun Feng
2024-09-27 19:23 ` Jonas Oberhauser
2024-09-27 20:10 ` Mathieu Desnoyers
2024-09-27 22:18 ` Jonas Oberhauser
2024-09-28 22:10 ` Alan Huang
2024-09-28 23:12 ` Alan Huang
2024-09-25 12:19 ` Jonas Oberhauser
2024-09-17 14:34 ` [RFC PATCH 2/4] refscale: Add benchmarks for hazptr Boqun Feng
2024-09-17 14:34 ` [RFC PATCH 3/4] refscale: Add benchmarks for percpu_ref Boqun Feng
2024-09-17 14:34 ` [RFC PATCH 4/4] WIP: hazptr: Add hazptr test sample Boqun Feng
2024-09-18 7:18 ` [RFC PATCH 0/4] Add hazard pointers to kernel Linus Torvalds
2024-09-18 22:44 ` Neeraj Upadhyay
2024-09-19 6:46 ` Linus Torvalds
2024-09-20 5:00 ` Neeraj Upadhyay
2024-09-19 14:30 ` Mateusz Guzik
2024-09-19 14:14 ` Christoph Hellwig
2024-09-19 14:21 ` Linus Torvalds
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