From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932439AbeAXArg (ORCPT ); Tue, 23 Jan 2018 19:47:36 -0500 Received: from mail-io0-f195.google.com ([209.85.223.195]:34892 "EHLO mail-io0-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932083AbeAXAre (ORCPT ); Tue, 23 Jan 2018 19:47:34 -0500 X-Google-Smtp-Source: AH8x225q5YgclDxTN+ZcXTYzj2KEN7i7UydmzCpJrSQ56KHltbknWmnoC5xoKs8WN02eHK4meKb03g== Message-ID: <1516754851.18068.3.camel@gmail.com> Subject: Re: [PATCH 1/4] lockd: convert nlm_host.h_count from atomic_t to refcount_t From: Trond Myklebust To: "J. Bruce Fields" , "Reshetova, Elena" Cc: "linux-nfs@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "jlayton@kernel.org" , "anna.schumaker@netapp.com" , "peterz@infradead.org" , "keescook@chromium.org" Date: Tue, 23 Jan 2018 19:47:31 -0500 In-Reply-To: <20180123220950.GA5632@fieldses.org> References: <1511954146-11793-1-git-send-email-elena.reshetova@intel.com> <1511954146-11793-2-git-send-email-elena.reshetova@intel.com> <20171221202350.GE31467@fieldses.org> <2236FBA76BA1254E88B949DDB74E612B802CFB57@IRSMSX102.ger.corp.intel.com> <20171222142553.GA9630@fieldses.org> <20171222154250.GB9630@fieldses.org> <2236FBA76BA1254E88B949DDB74E612B802D08DA@IRSMSX102.ger.corp.intel.com> <20180123220950.GA5632@fieldses.org> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.26.4 (3.26.4-1.fc27) 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 Tue, 2018-01-23 at 17:09 -0500, J. Bruce Fields wrote: > > The object still has useful information in it so we can't just > reinitalize it completely. I guess we could make nlm_get_host do > > if (refcount_read(&host->h_count)) > refcount_inc(&host->h_count); > else > refcount_set(&host->h_count, 1); > > Or we could just change the code so the refcount is always 1 higher > in > the NFS server case, so "1" instead of "0" is used to mean "nobody's > using this, you can garbage collect this", and then it won't go to 0 > until the garbage collector actually destroys it. > > This isn't an unusual pattern, what have other subsystems been doing? > Hi Bruce, Sorry I forgot about the issues with the server garbage collector, and I applied these patches to my linux-next a couple of weeks ago. What say we fix the issue with something like the following? 8<------------------------------------------------------------ >>From 83ce0f55ca54337a573f1d70038714815a9cd645 Mon Sep 17 00:00:00 2001 From: Trond Myklebust Date: Tue, 23 Jan 2018 19:39:04 -0500 Subject: [PATCH] lockd: Fix server refcounting The server shouldn't actually delete the struct nlm_host until it hits the garbage collector. In order to make that work correctly with the refcount API, we can bump the refcount by one, and then use refcount_dec_if_one() in the garbage collector. Signed-off-by: Trond Myklebust --- fs/lockd/host.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/fs/lockd/host.c b/fs/lockd/host.c index 7d6ab72bbe65..d35cd6be0675 100644 --- a/fs/lockd/host.c +++ b/fs/lockd/host.c @@ -388,6 +388,8 @@ struct nlm_host *nlmsvc_lookup_host(const struct svc_rqst *rqstp, ln->nrhosts++; nrhosts++; + refcount_inc(&host->h_count); + dprintk("lockd: %s created host %s (%s)\n", __func__, host->h_name, host->h_addrbuf); @@ -662,8 +664,7 @@ nlm_gc_hosts(struct net *net) for_each_host_safe(host, next, chain, nlm_server_hosts) { if (net && host->net != net) continue; - if (refcount_read(&host->h_count) || host->h_inuse - || time_before(jiffies, host->h_expires)) { + if (host->h_inuse || time_before(jiffies, host->h_expires)) { dprintk("nlm_gc_hosts skipping %s " "(cnt %d use %d exp %ld net %x)\n", host->h_name, refcount_read(&host->h_count), @@ -671,7 +672,8 @@ nlm_gc_hosts(struct net *net) host->net->ns.inum); continue; } - nlm_destroy_host_locked(host); + if (refcount_dec_if_one(&host->h_count)) + nlm_destroy_host_locked(host); } if (net) { -- 2.14.3 -- Trond Myklebust Linux NFS client maintainer, PrimaryData trond.myklebust@primarydata.com