From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757032Ab3BKMmR (ORCPT ); Mon, 11 Feb 2013 07:42:17 -0500 Received: from mx1.redhat.com ([209.132.183.28]:33973 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756914Ab3BKMmO (ORCPT ); Mon, 11 Feb 2013 07:42:14 -0500 Organization: Red Hat UK Ltd. Registered Address: Red Hat UK Ltd, Amberley Place, 107-111 Peascod Street, Windsor, Berkshire, SI4 1TE, United Kingdom. Registered in England and Wales under Company Registration No. 3798903 From: David Howells In-Reply-To: <20130122073315.13822.27093.stgit@srivatsabhat.in.ibm.com> References: <20130122073315.13822.27093.stgit@srivatsabhat.in.ibm.com> <20130122073210.13822.50434.stgit@srivatsabhat.in.ibm.com> To: "Srivatsa S. Bhat" Cc: dhowells@redhat.com, tglx@linutronix.de, peterz@infradead.org, tj@kernel.org, oleg@redhat.com, paulmck@linux.vnet.ibm.com, rusty@rustcorp.com.au, mingo@kernel.org, akpm@linux-foundation.org, namhyung@kernel.org, rostedt@goodmis.org, wangyun@linux.vnet.ibm.com, xiaoguangrong@linux.vnet.ibm.com, rjw@sisk.pl, sbw@mit.edu, fweisbec@gmail.com, linux@arm.linux.org.uk, nikunj@linux.vnet.ibm.com, linux-pm@vger.kernel.org, linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, netdev@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v5 01/45] percpu_rwlock: Introduce the global reader-writer lock backend Date: Mon, 11 Feb 2013 12:41:31 +0000 Message-ID: <30708.1360586491@warthog.procyon.org.uk> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Srivatsa S. Bhat wrote: > We can use global rwlocks as shown below safely, without fear of deadlocks: > > Readers: > > CPU 0 CPU 1 > ------ ------ > > 1. spin_lock(&random_lock); read_lock(&my_rwlock); > > > 2. read_lock(&my_rwlock); spin_lock(&random_lock); The lock order on CPU 0 is unsafe if CPU2 can do: write_lock(&my_rwlock); spin_lock(&random_lock); and on CPU 1 if CPU2 can do: spin_lock(&random_lock); write_lock(&my_rwlock); I presume you were specifically excluding these situations? David From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx1.redhat.com (mx1.redhat.com [209.132.183.28]) by ozlabs.org (Postfix) with ESMTP id DE1572C02C7 for ; Mon, 11 Feb 2013 23:42:07 +1100 (EST) From: David Howells In-Reply-To: <20130122073315.13822.27093.stgit@srivatsabhat.in.ibm.com> References: <20130122073315.13822.27093.stgit@srivatsabhat.in.ibm.com> <20130122073210.13822.50434.stgit@srivatsabhat.in.ibm.com> To: "Srivatsa S. Bhat" Subject: Re: [PATCH v5 01/45] percpu_rwlock: Introduce the global reader-writer lock backend Date: Mon, 11 Feb 2013 12:41:31 +0000 Message-ID: <30708.1360586491@warthog.procyon.org.uk> Cc: linux-doc@vger.kernel.org, peterz@infradead.org, fweisbec@gmail.com, linux-kernel@vger.kernel.org, dhowells@redhat.com, mingo@kernel.org, linux-arch@vger.kernel.org, linux@arm.linux.org.uk, xiaoguangrong@linux.vnet.ibm.com, wangyun@linux.vnet.ibm.com, paulmck@linux.vnet.ibm.com, nikunj@linux.vnet.ibm.com, linux-pm@vger.kernel.org, rusty@rustcorp.com.au, rostedt@goodmis.org, rjw@sisk.pl, namhyung@kernel.org, tglx@linutronix.de, linux-arm-kernel@lists.infradead.org, netdev@vger.kernel.org, oleg@redhat.com, sbw@mit.edu, tj@kernel.org, akpm@linux-foundation.org, linuxppc-dev@lists.ozlabs.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Srivatsa S. Bhat wrote: > We can use global rwlocks as shown below safely, without fear of deadlocks: > > Readers: > > CPU 0 CPU 1 > ------ ------ > > 1. spin_lock(&random_lock); read_lock(&my_rwlock); > > > 2. read_lock(&my_rwlock); spin_lock(&random_lock); The lock order on CPU 0 is unsafe if CPU2 can do: write_lock(&my_rwlock); spin_lock(&random_lock); and on CPU 1 if CPU2 can do: spin_lock(&random_lock); write_lock(&my_rwlock); I presume you were specifically excluding these situations? David From mboxrd@z Thu Jan 1 00:00:00 1970 From: dhowells@redhat.com (David Howells) Date: Mon, 11 Feb 2013 12:41:31 +0000 Subject: [PATCH v5 01/45] percpu_rwlock: Introduce the global reader-writer lock backend In-Reply-To: <20130122073315.13822.27093.stgit@srivatsabhat.in.ibm.com> References: <20130122073315.13822.27093.stgit@srivatsabhat.in.ibm.com> <20130122073210.13822.50434.stgit@srivatsabhat.in.ibm.com> Message-ID: <30708.1360586491@warthog.procyon.org.uk> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org Srivatsa S. Bhat wrote: > We can use global rwlocks as shown below safely, without fear of deadlocks: > > Readers: > > CPU 0 CPU 1 > ------ ------ > > 1. spin_lock(&random_lock); read_lock(&my_rwlock); > > > 2. read_lock(&my_rwlock); spin_lock(&random_lock); The lock order on CPU 0 is unsafe if CPU2 can do: write_lock(&my_rwlock); spin_lock(&random_lock); and on CPU 1 if CPU2 can do: spin_lock(&random_lock); write_lock(&my_rwlock); I presume you were specifically excluding these situations? David