From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933312AbaGPDmR (ORCPT ); Tue, 15 Jul 2014 23:42:17 -0400 Received: from out3-smtp.messagingengine.com ([66.111.4.27]:53839 "EHLO out3-smtp.messagingengine.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933191AbaGPDmP (ORCPT ); Tue, 15 Jul 2014 23:42:15 -0400 X-Sasl-enc: fpT07VH6iDxLWnVCllcwXeZym1Nth+v1ZqaJdV0V8e7k 1405482134 Message-ID: <1405482132.2527.26.camel@perseus.fritz.box> Subject: Re: [PATCH 6/6] autofs4: don't take spinlock when not needed in autofs4_lookup_expiring From: Ian Kent To: NeilBrown Cc: autofs@vger.kernel.org, linux-kernel@vger.kernel.org Date: Wed, 16 Jul 2014 11:42:12 +0800 In-Reply-To: <20140709234114.4525.70534.stgit@notabene.brown> References: <20140709233541.4525.25151.stgit@notabene.brown> <20140709234114.4525.70534.stgit@notabene.brown> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.10.4 (3.10.4-2.fc20) Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2014-07-10 at 09:41 +1000, NeilBrown wrote: > If the expiring_list is empty, we can avoid a costly spinlock > in the rcu-walk path through authfs4_d_manage. > > Signed-off-by: NeilBrown I know it should be straight forward to say this is OK but I always think twice and again about areas that are subject to race pressure, such as the expire to mount pressure of this code. After thinking about it for a while now I don't have any reason to think this would be a problem. Perhaps later pressure testing will reveal something I missed. It occurs to me that autofs4_lookup_active() might benefit from a similar addition. Multiple calls to ->lookup() made while the dentry is still unhashed should have enforced ordering due to the directory i_mutex so there shouldn't be a problem adding this. But perhaps you haven't seen delays in that function. Acked-by: Ian Kent > --- > fs/autofs4/root.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/fs/autofs4/root.c b/fs/autofs4/root.c > index 1ad119407e2f..774c2dab331b 100644 > --- a/fs/autofs4/root.c > +++ b/fs/autofs4/root.c > @@ -219,6 +219,8 @@ static struct dentry *autofs4_lookup_expiring(struct dentry *dentry, > const unsigned char *str = name->name; > struct list_head *p, *head; > > + if (list_empty(&sbi->expiring_list)) > + return NULL; > spin_lock(&sbi->lookup_lock); > head = &sbi->expiring_list; > list_for_each(p, head) { > >