From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ingo Molnar Subject: Re: [PATCH 17/19] locking/barriers: Kill lockless_dereference Date: Tue, 24 Oct 2017 11:31:04 +0200 Message-ID: <20171024093104.rukpl26fukj7bxvg@gmail.com> References: <20171023210408.GA2930@linux.vnet.ibm.com> <1508792849-3115-17-git-send-email-paulmck@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <1508792849-3115-17-git-send-email-paulmck@linux.vnet.ibm.com> Sender: linux-kernel-owner@vger.kernel.org To: "Paul E. McKenney" Cc: linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, will.deacon@arm.com, mark.rutland@arm.com, snitzer@redhat.com, thor.thayer@linux.intel.com, viro@zeniv.linux.org.uk, davem@davemloft.net, shuah@kernel.org, mpe@ellerman.id.au, tj@kernel.org, torvalds@linux-foundation.org List-Id: linux-arch.vger.kernel.org * Paul E. McKenney wrote: > From: Will Deacon > > lockless_dereference is a nice idea, but its gained little traction in > kernel code since it's introduction three years ago. This is partly s/its/it s/it's/its > because it's a pain to type, but also because using READ_ONCE instead > will work correctly on all architectures apart from Alpha, which is a > fully supported but somewhat niche architecture these days. > > This patch moves smp_read_barrier_depends() (a NOP on all architectures > other than Alpha) from lockless_dereference into READ_ONCE, converts > the few actual users over to READ_ONCE and then finally removes > lockless_dereference altogether. Nit: if we refer to smp_read_barrier_depends() with parentheses (which is the nice thing to do for function-alike symbols), then we should do the same with READ_ONCE() and lockless_dereference() as well. Also, could we please split this into three patches: #1: Add smp_read_barrier_depends() to READ_ONCE() #2: Convert all lockless_dereference() users to READ_ONCE() #3: Remove the now unused lockless_dereference() API to make it easier to analyze if bisected to, should any problems arise? Thanks, Ingo