From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtpout.efficios.com (smtpout.efficios.com [167.114.26.122]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 9A87A1DA26; Mon, 7 Oct 2024 14:54:11 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=167.114.26.122 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1728312853; cv=none; b=hOocJ4yOlq7FSY3lSpQkZt75kJzBpvPAe/43cg+0nOw97Iv9llgo3Q01pShneylo/fdmhqzONDVWErFlowqsXDI65aK/9SzSnoy3iA3CtXdgYu3Yf7HhtWKNoy+WJz5CxdsUjVeehJKlGc271D4swWurfoRIQqO3zNtckmp1tR4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1728312853; c=relaxed/simple; bh=sihbyG/v8McdrExFlMF4l5W4opSu7i5ut7iK0mpnEh8=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=ek3Z9MxGOur2utUXPR7uYCeHQPZP1cdvPezlFyD6VmsPfLWVEXN1VzHT4lQ7/cDu3l6SCCImHn4CjjfOIsY+Z4d2jwICaQHiVMoxtovrulCOYT8OxyimfER5oBznZdOIsRf6LcHEHoSqUKdszfMW/mbwlGSB6vowkj9d8MdWwXA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=efficios.com; spf=pass smtp.mailfrom=efficios.com; dkim=pass (2048-bit key) header.d=efficios.com header.i=@efficios.com header.b=VVbZsMaT; arc=none smtp.client-ip=167.114.26.122 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=efficios.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=efficios.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=efficios.com header.i=@efficios.com header.b="VVbZsMaT" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=efficios.com; s=smtpout1; t=1728312850; bh=sihbyG/v8McdrExFlMF4l5W4opSu7i5ut7iK0mpnEh8=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=VVbZsMaTm+kJ+mJ61HRGRpZ1hTwl6/ALHHgD0lC47SzwRONtiKJDP/owbxPIJ+I1t GYhhI0in/OnM8yY6y+4C4JufX3rNF6tnmGUFxS34BeyhyE4zscpqNdh/LogWI9pG70 j7L26qV3xBABIsUZOHvjrGFRO/NKwbYhUdT9Bg8wzlnGYm4eq7ZMhreaqgZ1t9JqhX E6ucijPLbq5BlRs+yPP4gInxeIHHwJgDBxfmhI4Kk346JdqkkhEI72IFYXlFwpZ3eZ e9hEEOIF9AqQSTpznimryYAmopYOU4GA1EUTF/ZNC0QBOGBsCgbfUz45hQ6ici00a3 dnk+p+fdadBCQ== Received: from [172.16.0.134] (96-127-217-162.qc.cable.ebox.net [96.127.217.162]) by smtpout.efficios.com (Postfix) with ESMTPSA id 4XMhxZ2Smtz3DX; Mon, 7 Oct 2024 10:54:10 -0400 (EDT) Message-ID: Date: Mon, 7 Oct 2024 10:52:12 -0400 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 3/4] hp: Implement Hazard Pointers To: Boqun Feng Cc: Linus Torvalds , Andrew Morton , Peter Zijlstra , linux-kernel@vger.kernel.org, Nicholas Piggin , Michael Ellerman , Greg Kroah-Hartman , Sebastian Andrzej Siewior , "Paul E. McKenney" , Will Deacon , Alan Stern , John Stultz , Neeraj Upadhyay , Frederic Weisbecker , Joel Fernandes , Josh Triplett , Uladzislau Rezki , Steven Rostedt , Lai Jiangshan , Zqiang , Ingo Molnar , Waiman Long , Mark Rutland , Thomas Gleixner , Vlastimil Babka , maged.michael@gmail.com, Mateusz Guzik , Jonas Oberhauser , rcu@vger.kernel.org, linux-mm@kvack.org, lkmm@lists.linux.dev References: <20241002010205.1341915-1-mathieu.desnoyers@efficios.com> <20241002010205.1341915-4-mathieu.desnoyers@efficios.com> From: Mathieu Desnoyers Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 2024-10-07 15:47, Boqun Feng wrote: > On Thu, Oct 03, 2024 at 09:30:53AM -0400, Mathieu Desnoyers wrote: > [...] >>>> + /* >>>> + * Use RCU dereference without lockdep checks, because >>>> + * lockdep is not aware of HP guarantees. >>>> + */ >>>> + addr2 = rcu_access_pointer(*addr_p); /* Load A */ >>> >>> Why rcu_access_pointer() instead of READ_ONCE()? Because you want to >>> mark the head of address dependency? >> >> Yes, the intent here is to mark the address dependency and provide >> a publication guarantee similar to RCU pairing rcu_assign_pointer >> and rcu_dereference. Do you see any reason why READ_ONCE() would >> suffice here ? > > READ_ONCE() also provides address dependencies. See the "DEPENDENCY > RELATIONS: data, addr, and ctrl" section in > tools/memory-model/Documentation/explanantion.txt. Fair point, so let's use READ_ONCE() then. Thanks, Mathieu > > Regards, > Boqun > >> >> Thanks, >> >> Mathieu >> -- Mathieu Desnoyers EfficiOS Inc. https://www.efficios.com