From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr0-f199.google.com (mail-wr0-f199.google.com [209.85.128.199]) by kanga.kvack.org (Postfix) with ESMTP id 680CB6B0006 for ; Wed, 23 May 2018 08:50:13 -0400 (EDT) Received: by mail-wr0-f199.google.com with SMTP id u56-v6so16836240wrf.18 for ; Wed, 23 May 2018 05:50:13 -0700 (PDT) Received: from Galois.linutronix.de (Galois.linutronix.de. [2a01:7a0:2:106d:700::1]) by mx.google.com with ESMTPS id w10-v6si1678972wma.87.2018.05.23.05.50.12 for (version=TLS1_2 cipher=AES128-SHA bits=128/128); Wed, 23 May 2018 05:50:12 -0700 (PDT) Date: Wed, 23 May 2018 14:50:07 +0200 From: Sebastian Andrzej Siewior Subject: Re: [PATCH 3/8] md: raid5: use refcount_t for reference counting instead atomic_t Message-ID: <20180523125007.pbxcxef622cde3jz@linutronix.de> References: <20180509193645.830-1-bigeasy@linutronix.de> <20180509193645.830-4-bigeasy@linutronix.de> <20180523123615.GY12217@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20180523123615.GY12217@hirez.programming.kicks-ass.net> Sender: owner-linux-mm@kvack.org List-ID: To: Peter Zijlstra Cc: linux-kernel@vger.kernel.org, tglx@linutronix.de, Ingo Molnar , linux-mm@kvack.org, Shaohua Li , linux-raid@vger.kernel.org, Anna-Maria Gleixner On 2018-05-23 14:36:15 [+0200], Peter Zijlstra wrote: > > Most changes are 1:1 replacements except for > > BUG_ON(atomic_inc_return(&sh->count) != 1); > > That doesn't look right, 'inc_return == 1' implies inc-from-zero, which > is not allowed by refcount. > > > which has been turned into > > refcount_inc(&sh->count); > > BUG_ON(refcount_read(&sh->count) != 1); > > And that is racy, you can have additional increments in between. so do we stay with the atomic* API here or do we extend refcount* API? Sebastian