Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751721AbZFXEJt (ORCPT ); Wed, 24 Jun 2009 00:09:49 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750792AbZFXEJl (ORCPT ); Wed, 24 Jun 2009 00:09:41 -0400 Received: from TYO202.gate.nec.co.jp ([202.32.8.206]:53738 "EHLO tyo202.gate.nec.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750721AbZFXEJk (ORCPT ); Wed, 24 Jun 2009 00:09:40 -0400 Date: Wed, 24 Jun 2009 13:05:12 +0900 From: Daisuke Nishimura To: KAMEZAWA Hiroyuki Cc: nishimura@mxp.nes.nec.co.jp, "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , "balbir@linux.vnet.ibm.com" , "lizf@cn.fujitsu.com" , "menage@google.com" , "akpm@linux-foundation.org" Subject: Re: [PATCH 1/2] memcg: cgroup fix rmdir hang Message-Id: <20090624130512.9e4550c4.nishimura@mxp.nes.nec.co.jp> In-Reply-To: <20090623160854.93abeecb.kamezawa.hiroyu@jp.fujitsu.com> References: <20090623160720.36230fa2.kamezawa.hiroyu@jp.fujitsu.com> <20090623160854.93abeecb.kamezawa.hiroyu@jp.fujitsu.com> Organization: NEC Soft, Ltd. X-Mailer: Sylpheed 2.6.0 (GTK+ 2.10.14; i686-pc-mingw32) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 6324 Lines: 166 On Tue, 23 Jun 2009 16:08:54 +0900, KAMEZAWA Hiroyuki wrote: > From: KAMEZAWA Hiroyuki > > Now, cgroup has a logic to wait until ready-to-rmdir for avoiding > frequent -EBUSY at rmdir. > (See Commit ec64f51545fffbc4cb968f0cea56341a4b07e85a > cgroup: fix frequent -EBUSY at rmdir. > > Nishimura-san reported bad case for waiting and This is a fix to > make it reliable. A thread waiting for thread cannot be waken up > when a refcnt gotten by css_tryget() isn't put immediately. > (Original code assumed css_put() will be called soon.) > > memcg has this case and this is a fix for the problem. This adds > retry_rmdir() callback to subsys and check we can sleep or not. > > Note: another solution will be adding "rmdir state" to subsys. > But it will be much complicated than this do-enough-check solution. > > Changelog v1 -> v2: > - splitted into 2 patches. This just includes retry_rmdir() modification. > > Reported-by: Daisuke Nishimura > Signed-off-by: KAMEZAWA Hiroyuki Looks good to me. Reviewed-by: Daisuke Nishimura I've been testing with [2/2] applied (because both of these patches are necessary to fix this problem completely), and it works fine so far. But I want to test in more test cases. Thanks, Daisuke Nishimura. > --- > Documentation/cgroups/cgroups.txt | 11 +++++++++++ > include/linux/cgroup.h | 1 + > kernel/cgroup.c | 20 +++++++++++++++++++- > mm/memcontrol.c | 14 ++++++++++++-- > 4 files changed, 43 insertions(+), 3 deletions(-) > > Index: fix-rmdir-cgroup/include/linux/cgroup.h > =================================================================== > --- fix-rmdir-cgroup.orig/include/linux/cgroup.h > +++ fix-rmdir-cgroup/include/linux/cgroup.h > @@ -374,6 +374,7 @@ struct cgroup_subsys { > struct cgroup_subsys_state *(*create)(struct cgroup_subsys *ss, > struct cgroup *cgrp); > int (*pre_destroy)(struct cgroup_subsys *ss, struct cgroup *cgrp); > + int (*retry_rmdir)(struct cgroup_subsys *ss, struct cgroup *cgrp); > void (*destroy)(struct cgroup_subsys *ss, struct cgroup *cgrp); > int (*can_attach)(struct cgroup_subsys *ss, > struct cgroup *cgrp, struct task_struct *tsk); > Index: fix-rmdir-cgroup/kernel/cgroup.c > =================================================================== > --- fix-rmdir-cgroup.orig/kernel/cgroup.c > +++ fix-rmdir-cgroup/kernel/cgroup.c > @@ -636,6 +636,23 @@ static int cgroup_call_pre_destroy(struc > } > return ret; > } > +/* > + * Call subsys's retry_rmdir() handler. If this returns non-Zero, we retry > + * rmdir immediately and call pre_destroy again. > + */ > +static int cgroup_check_retry_rmdir(struct cgroup *cgrp) > +{ > + struct cgroup_subsys *ss; > + int ret = 0; > + > + for_each_subsys(cgrp->root, ss) > + if (ss->pre_destroy) { > + ret = ss->retry_rmdir(ss, cgrp); > + if (ret) > + break; > + } > + return ret; > +} > > static void free_cgroup_rcu(struct rcu_head *obj) > { > @@ -2722,7 +2739,8 @@ again: > > if (!cgroup_clear_css_refs(cgrp)) { > mutex_unlock(&cgroup_mutex); > - schedule(); > + if (!cgroup_check_retry_rmdir(cgrp)) > + schedule(); > finish_wait(&cgroup_rmdir_waitq, &wait); > clear_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags); > if (signal_pending(current)) > Index: fix-rmdir-cgroup/mm/memcontrol.c > =================================================================== > --- fix-rmdir-cgroup.orig/mm/memcontrol.c > +++ fix-rmdir-cgroup/mm/memcontrol.c > @@ -1457,8 +1457,6 @@ __mem_cgroup_commit_charge_swapin(struct > } > rcu_read_unlock(); > } > - /* add this page(page_cgroup) to the LRU we want. */ > - > } > > void mem_cgroup_commit_charge_swapin(struct page *page, struct mem_cgroup *ptr) > @@ -2571,6 +2569,17 @@ static int mem_cgroup_pre_destroy(struct > return mem_cgroup_force_empty(mem, false); > } > > +static int mem_cgroup_retry_rmdir(struct cgroup_subsys *ss, > + struct cgroup *cont) > +{ > + struct mem_cgroup *mem = mem_cgroup_from_cont(cont); > + > + if (res_counter_read_u64(&mem->res, RES_USAGE)) > + return 1; > + return 0; > +} > + > + > static void mem_cgroup_destroy(struct cgroup_subsys *ss, > struct cgroup *cont) > { > @@ -2610,6 +2619,7 @@ struct cgroup_subsys mem_cgroup_subsys = > .subsys_id = mem_cgroup_subsys_id, > .create = mem_cgroup_create, > .pre_destroy = mem_cgroup_pre_destroy, > + .retry_rmdir = mem_cgroup_retry_rmdir, > .destroy = mem_cgroup_destroy, > .populate = mem_cgroup_populate, > .attach = mem_cgroup_move_task, > Index: fix-rmdir-cgroup/Documentation/cgroups/cgroups.txt > =================================================================== > --- fix-rmdir-cgroup.orig/Documentation/cgroups/cgroups.txt > +++ fix-rmdir-cgroup/Documentation/cgroups/cgroups.txt > @@ -500,6 +500,17 @@ there are not tasks in the cgroup. If pr > rmdir() will fail with it. From this behavior, pre_destroy() can be > called multiple times against a cgroup. > > +int retry_rmdir(struct cgroup_subsys *ss, struct cgroup *cgrp); > + > +Called at rmdir right after the kernel finds there are remaining refcnt on > +subsystems after pre_destroy(). When retry_rmdir() returns 0, the caller enter > +sleep and wakes up when css's refcnt goes down to 0 by css_put(). > +When this returns 1, the caller doesn't sleep and retry rmdir immediately. > +This is useful when the subsys knows remaining css's refcnt is not temporal > +and to calling pre_destroy() again is proper way to remove that. > +(or proper way to retrun -EBUSY.) > + > + > int can_attach(struct cgroup_subsys *ss, struct cgroup *cgrp, > struct task_struct *task) > (cgroup_mutex held by caller) > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@kvack.org. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: email@kvack.org -- 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/