Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752198Ab1DRLmZ (ORCPT ); Mon, 18 Apr 2011 07:42:25 -0400 Received: from mail-vx0-f174.google.com ([209.85.220.174]:48701 "EHLO mail-vx0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751290Ab1DRLmS convert rfc822-to-8bit (ORCPT ); Mon, 18 Apr 2011 07:42:18 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; b=j6tSVW44AuGTYJ+Sn+OAvyzg2d6ZHiNVWzlmgu8iuTIYe25AdaV+LrljQKLPAdYYoe 44T+wmmE6F0QrqAIAmsrR0ESZrCwRjfJeTMqDT1NAQjc4ws2S35Rrq6R56NjK38Jd0mf ioq3gNuhhAgu4uuptj+si6QF7AhxTJU/H4jMU= MIME-Version: 1.0 In-Reply-To: <20110415174451.GB19644@Krystal> References: <1302684835-14133-1-git-send-email-ying.huang@intel.com> <1302684835-14133-4-git-send-email-ying.huang@intel.com> <20110413210757.GA11683@Krystal> <4DA7903B.5030508@intel.com> <20110415164629.GA13983@Krystal> <20110415174320.GA2283@linux.vnet.ibm.com> <20110415174451.GB19644@Krystal> Date: Mon, 18 Apr 2011 19:42:16 +0800 Message-ID: Subject: Re: [PATCH -v3 3/4] lib, Make gen_pool memory allocator lockless From: huang ying To: "Paul E. McKenney" Cc: Huang Ying , Len Brown , "linux-kernel@vger.kernel.org" , Andi Kleen , "Luck, Tony" , "linux-acpi@vger.kernel.org" , Andrew Morton , Mathieu Desnoyers Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2610 Lines: 54 Hi, Paul, On Sat, Apr 16, 2011 at 1:44 AM, Mathieu Desnoyers wrote: > * Paul E. McKenney (paulmck@linux.vnet.ibm.com) wrote: >> On Fri, Apr 15, 2011 at 12:46:29PM -0400, Mathieu Desnoyers wrote: >> > * Huang Ying (ying.huang@intel.com) wrote: >> > > On 04/14/2011 05:07 AM, Mathieu Desnoyers wrote: >> > > > * Huang Ying (ying.huang@intel.com) wrote: >> > > > [...] >> > > >> + * rcu_read_lock and rcu_read_unlock is not used int gen_pool_alloc, >> > > >> + * gen_pool_free, gen_pool_avail and gen_pool_size etc, because chunks >> > > >> + * are only added into pool, not deleted from pool unless the pool >> > > >> + * itself is destroyed.  If chunk will be deleted from pool, >> > > >> + * rcu_read_lock and rcu_read_unlock should be uses in these >> > > >> + * functions. >> > > > >> > > > So how do you protect between pool destruction and adding chunks into >> > > > the pool ? >> > > >> > > Because the pool itself will be freed when destruction, we need some >> > > mechanism outside of pool.  For example, if gen_pool_add() is called via >> > > device file IOCTL, we must un-register the device file first, and >> > > destroy the pool after the last reference to device has gone. >> > >> > I am concerned about the list_for_each_entry_rcu() (and thus >> > rcu_dereference_raw()) used outside of rcu_read_lock/unlock pairs. >> > Validation infrastructure as recently been added to RCU: it triggers >> > warnings when these situations are encountered in some RCU debugging >> > configurations. The case of RCU list iteration is not covered by the >> > checks, but it would make sense to be aware of it. >> > >> > So although it seems like your code does not require rcu read lock >> > critical sections, I'd prefer to let Paul McKenney have a look. >> >> As long as you add elements and never remove them, then you can get >> away with using list_for_each_entry_rcu() outside of an RCU read-side >> critical section.  But please comment this -- it is all too easy >> for someone to decide later to start deleting elements without also >> inserting the needed rcu_read_lock() and rcu_read_unlock() pairs. >> >> But I have lost the thread -- what code am I supposed to look at? > > You can have a look at https://lkml.org/lkml/2011/4/13/56 What do you think about this patch and its usage of RCU? Best Regards, Huang Ying -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/