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 <urezki@gmail.com>,
Steven 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>
Subject: Re: [RFC PATCH 1/4] hazptr: Add initial implementation of hazard pointers
Date: Thu, 26 Sep 2024 09:12:58 -0700 [thread overview]
Message-ID: <CAHk-=wjL803+FxtAPSGrWqThGQP5cCHzzwZJFq+-fkgt5DQ3VQ@mail.gmail.com> (raw)
In-Reply-To: <55633835-242c-4d7f-875b-24b16f17939c@huaweicloud.com>
On Thu, 26 Sept 2024 at 08:54, Jonas Oberhauser
<jonas.oberhauser@huaweicloud.com> wrote:
>
> No, the issue introduced by the compiler optimization (or by your
> original patch) is that the CPU can speculatively load from the first
> pointer as soon as it has completed the load of that pointer:
You mean the compiler can do it. The inline asm has no impact on what
the CPU does. The conditional isn't a barrier for the actual hardware.
But once the compiler doesn't try to do it, the data dependency on the
address does end up being an ordering constraint on the hardware too
(I'm happy to say that I haven't heard from the crazies that want
value prediction in a long time).
Just use a barrier. Or make sure to use the proper ordered memory
accesses when possible. Don't use an inline asm for the compare - we
don't even have anything insane like that as a portable helper, and we
shouldn't have it.
Linus
next prev parent reply other threads:[~2024-09-26 16:13 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 [this message]
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
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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