linux-kernel - Re: [RFC PATCH v2 3/4] hp: Implement Hazard Pointers

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Message-ID: <812121c6-734d-4f68-b808-d3fa7c380604@efficios.com>
Date: Mon, 7 Oct 2024 09:22:52 -0400
From: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Boqun Feng <boqun.feng@...il.com>, linux-kernel@...r.kernel.org,
 Linus Torvalds <torvalds@...ux-foundation.org>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Nicholas Piggin <npiggin@...il.com>, Michael Ellerman <mpe@...erman.id.au>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
 "Paul E. McKenney" <paulmck@...nel.org>, Will Deacon <will@...nel.org>,
 Alan Stern <stern@...land.harvard.edu>, 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>,
 Jonas Oberhauser <jonas.oberhauser@...weicloud.com>, rcu@...r.kernel.org,
 linux-mm@...ck.org, lkmm@...ts.linux.dev
Subject: Re: [RFC PATCH v2 3/4] hp: Implement Hazard Pointers

On 2024-10-07 12:42, Peter Zijlstra wrote:
> On Sat, Oct 05, 2024 at 02:56:26PM -0400, Mathieu Desnoyers wrote:
>> On 2024-10-05 18:07, Peter Zijlstra wrote:
>>> On Sat, Oct 05, 2024 at 06:04:44PM +0200, Peter Zijlstra wrote:
>>>> On Fri, Oct 04, 2024 at 02:27:33PM -0400, Mathieu Desnoyers wrote:
>>>
>>>>> +void hp_scan(struct hp_slot __percpu *percpu_slots, void *addr,
>>>>> +	     void (*retire_cb)(int cpu, struct hp_slot *slot, void *addr))
>>>>> +{
>>>>> +	int cpu;
>>>>> +
>>>>> +	/*
>>>>> +	 * Store A precedes hp_scan(): it unpublishes addr (sets it to
>>>>> +	 * NULL or to a different value), and thus hides it from hazard
>>>>> +	 * pointer readers.
>>>>> +	 */
>>>
>>> This should probably assert we're in a preemptible context. Otherwise
>>> people will start using this in non-preemptible context and then we get
>>> to unfuck things later.
>>
>> Something like this ?
>>
>> +       /* Should only be called from preemptible context. */
>> +       WARN_ON_ONCE(in_atomic());
> 
> 	lockdep_assert_preemption_enabled();
> 
> that also checks local IRQ state IIRC.

I'll use this instead, thanks!

Mathieu

-- 
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com