From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx3-rdu2.redhat.com ([66.187.233.73]:34508 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752668AbeEOSfi (ORCPT ); Tue, 15 May 2018 14:35:38 -0400 Subject: Re: [PATCH v3 2/2] locking/percpu-rwsem: Annotate rwsem ownership transfer by setting RWSEM_OWNER_UNKNOWN To: Peter Zijlstra Cc: Ingo Molnar , Thomas Gleixner , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Davidlohr Bueso , "Theodore Y. Ts'o" , Oleg Nesterov , Amir Goldstein , Jan Kara , Matthew Wilcox References: <1526405884-4860-1-git-send-email-longman@redhat.com> <1526405884-4860-3-git-send-email-longman@redhat.com> <20180515175805.GN12217@hirez.programming.kicks-ass.net> <1baa1a1a-a4a7-d706-8c01-5ff6a8757f97@redhat.com> <20180515180549.GP12217@hirez.programming.kicks-ass.net> From: Waiman Long Message-ID: Date: Tue, 15 May 2018 14:35:33 -0400 MIME-Version: 1.0 In-Reply-To: <20180515180549.GP12217@hirez.programming.kicks-ass.net> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Content-Language: en-US Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On 05/15/2018 02:05 PM, Peter Zijlstra wrote: > On Tue, May 15, 2018 at 02:02:00PM -0400, Waiman Long wrote: >> On 05/15/2018 01:58 PM, Peter Zijlstra wrote: >>> On Tue, May 15, 2018 at 01:38:04PM -0400, Waiman Long wrote: >>>> +/* >>>> + * Owner value to indicate the rwsem's owner is not currently known. >>>> + */ >>>> +#define RWSEM_OWNER_UNKNOWN ((struct task_struct *)-1) >>> It might be nice to comment that this works and relies on having that >>> ANON_OWNER bit set. >> I am just trying not to expose internal working of rwsem, but I can >> document that one of the bits is the real deal without specifying which one. > Thing is, you don't want someone changing this without knowing about > that one magic bit. It doesn't hurt to be explicit here. > > Also, do we want -1L instead of a -1 literal? > Yes, I should -1L instead. Cheers, Longman