linux-kernel - Re: [PATCH 1/2] compiler.h: Introduce ptr

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Message-ID: <50bd6ecb-c8e3-4043-9040-b2b4ee71fc02@huaweicloud.com>
Date: Mon, 30 Sep 2024 14:06:12 +0200
From: Jonas Oberhauser <jonas.oberhauser@...weicloud.com>
To: paulmck@...nel.org
Cc: Alan Stern <stern@...land.harvard.edu>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Linus Torvalds <torvalds@...ux-foundation.org>,
 linux-kernel@...r.kernel.org, Greg Kroah-Hartman
 <gregkh@...uxfoundation.org>,
 Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
 Will Deacon <will@...nel.org>, Peter Zijlstra <peterz@...radead.org>,
 Boqun Feng <boqun.feng@...il.com>, John Stultz <jstultz@...gle.com>,
 Neeraj Upadhyay <Neeraj.Upadhyay@....com>,
 Frederic Weisbecker <frederic@...nel.org>,
 Joel Fernandes <joel@...lfernandes.org>,
 Josh Triplett <josh@...htriplett.org>, Uladzislau Rezki <urezki@...il.com>,
 Steven Rostedt <rostedt@...dmis.org>, Lai Jiangshan
 <jiangshanlai@...il.com>, Zqiang <qiang.zhang1211@...il.com>,
 Ingo Molnar <mingo@...hat.com>, Waiman Long <longman@...hat.com>,
 Mark Rutland <mark.rutland@....com>, Thomas Gleixner <tglx@...utronix.de>,
 Vlastimil Babka <vbabka@...e.cz>, maged.michael@...il.com,
 Mateusz Guzik <mjguzik@...il.com>, Gary Guo <gary@...yguo.net>,
 rcu@...r.kernel.org, linux-mm@...ck.org, lkmm@...ts.linux.dev
Subject: Re: [PATCH 1/2] compiler.h: Introduce ptr_eq() to preserve address
 dependency



Am 9/30/2024 um 1:04 PM schrieb Paul E. McKenney:
> On Mon, Sep 30, 2024 at 11:42:11AM +0200, Jonas Oberhauser wrote:
>>
>>
>> I also currently don't see any major difference between the constant and
>> register case. The point is that the address is known before loading into b,
>> and hence the compiler + hardware can speculatively load *b before loading
>> into b.
> 
> In theory, true.  In practice, in the register case, you need a little
> more bad luck for the compiler to be able to exploit your mistake.

If there's one thing I've never run out of, then it is bad luck with 
technology.

   jonas