Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755188AbZGBGa2 (ORCPT ); Thu, 2 Jul 2009 02:30:28 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751545AbZGBGaR (ORCPT ); Thu, 2 Jul 2009 02:30:17 -0400 Received: from e37.co.us.ibm.com ([32.97.110.158]:51153 "EHLO e37.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750896AbZGBGaO (ORCPT ); Thu, 2 Jul 2009 02:30:14 -0400 Date: Thu, 2 Jul 2009 12:00:05 +0530 From: Balbir Singh To: KAMEZAWA Hiroyuki Cc: "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , "nishimura@mxp.nes.nec.co.jp" , "menage@google.com" Subject: Re: [PATCH] memcg: fix cgroup rmdir hang v4 Message-ID: <20090702063002.GO11273@balbir.in.ibm.com> Reply-To: balbir@linux.vnet.ibm.com References: <20090630180109.f137c10e.kamezawa.hiroyu@jp.fujitsu.com> <20090701104747.afdcc6c7.kamezawa.hiroyu@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <20090701104747.afdcc6c7.kamezawa.hiroyu@jp.fujitsu.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 9013 Lines: 252 * KAMEZAWA Hiroyuki [2009-07-01 10:47:47]: > ok, here. > > == > From: KAMEZAWA Hiroyuki > > After commit: cgroup: fix frequent -EBUSY at rmdir > ec64f51545fffbc4cb968f0cea56341a4b07e85a > cgroup's rmdir (especially against memcg) doesn't return -EBUSY > by temporal ref counts. That commit expects all refs after pre_destroy() > is temporary but...it wasn't. Then, rmdir can wait permanently. > This patch tries to fix that and change followings. > Sorry for the late review, a few comments below > - set CGRP_WAIT_ON_RMDIR flag before pre_destroy(). > - clear CGRP_WAIT_ON_RMDIR flag when the subsys finds racy case. > if there are sleeping ones, wakes them up. > - rmdir() sleeps only when CGRP_WAIT_ON_RMDIR flag is set. > > Changelog v4->v5: > - added cgroup_exclude_rmdir(), cgroup_release_rmdir(). > > Changelog v3->v4: > - rewrite/add comments. > - remane cgroup_wakeup_rmdir_waiters() to cgroup_wakeup_rmdir_waiter(). > Changelog v2->v3: > - removed retry_rmdir() callback. > - make use of CGRP_WAIT_ON_RMDIR flag more. > > Reported-by: Daisuke Nishimura > Signed-off-by: KAMEZAWA Hiroyuki > --- > include/linux/cgroup.h | 14 ++++++++++++ > kernel/cgroup.c | 55 +++++++++++++++++++++++++++++++++---------------- > mm/memcontrol.c | 23 +++++++++++++++++--- > 3 files changed, 72 insertions(+), 20 deletions(-) > > Index: mmotm-2.6.31-Jun25/include/linux/cgroup.h > =================================================================== > --- mmotm-2.6.31-Jun25.orig/include/linux/cgroup.h > +++ mmotm-2.6.31-Jun25/include/linux/cgroup.h > @@ -366,6 +366,20 @@ int cgroup_task_count(const struct cgrou > int cgroup_is_descendant(const struct cgroup *cgrp, struct task_struct *task); > > /* > + * When the subsys has to access css and may add permanent refcnt to css, > + * it should take care of racy conditions with rmdir(). Following set of > + * functions, is for stop/restart rmdir if necessary. > + * Because these will call css_get/put, "css" should be alive css. > + * > + * cgroup_exclude_rmdir(); > + * ...do some jobs which may access arbitrary empty cgroup > + * cgroup_release_rmdir(); > + */ > + > +void cgroup_exclude_rmdir(struct cgroup_subsys_state *css); > +void cgroup_release_rmdir(struct cgroup_subsys_state *css); > + > +/* > * Control Group subsystem type. > * See Documentation/cgroups/cgroups.txt for details > */ > Index: mmotm-2.6.31-Jun25/kernel/cgroup.c > =================================================================== > --- mmotm-2.6.31-Jun25.orig/kernel/cgroup.c > +++ mmotm-2.6.31-Jun25/kernel/cgroup.c > @@ -734,16 +734,28 @@ static void cgroup_d_remove_dir(struct d > * reference to css->refcnt. In general, this refcnt is expected to goes down > * to zero, soon. > * > - * CGRP_WAIT_ON_RMDIR flag is modified under cgroup's inode->i_mutex; > + * CGRP_WAIT_ON_RMDIR flag is set under cgroup's inode->i_mutex; > */ > DECLARE_WAIT_QUEUE_HEAD(cgroup_rmdir_waitq); > > -static void cgroup_wakeup_rmdir_waiters(const struct cgroup *cgrp) > +static void cgroup_wakeup_rmdir_waiter(struct cgroup *cgrp) Should the function explictly mention rmdir? Also something like release_rmdir should be called release_and_wakeup to make the action clearer. Looks good to me otherwise and clean. > { > - if (unlikely(test_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags))) > + if (unlikely(test_and_clear_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags))) > wake_up_all(&cgroup_rmdir_waitq); > } > > +void cgroup_exclude_rmdir(struct cgroup_subsys_state *css) > +{ > + css_get(css); > +} > + > +void cgroup_release_rmdir(struct cgroup_subsys_state *css) > +{ > + cgroup_wakeup_rmdir_waiter(css->cgroup); > + css_put(css); > +} > + > + > static int rebind_subsystems(struct cgroupfs_root *root, > unsigned long final_bits) > { > @@ -1357,7 +1369,7 @@ int cgroup_attach_task(struct cgroup *cg > * wake up rmdir() waiter. the rmdir should fail since the cgroup > * is no longer empty. > */ > - cgroup_wakeup_rmdir_waiters(cgrp); > + cgroup_wakeup_rmdir_waiter(cgrp); > return 0; > } > > @@ -2696,33 +2708,42 @@ again: > mutex_unlock(&cgroup_mutex); > > /* > + * In general, subsystem has no css->refcnt after pre_destroy(). But > + * in racy cases, subsystem may have to get css->refcnt after > + * pre_destroy() and it makes rmdir return with -EBUSY. This sometimes > + * make rmdir return -EBUSY too often. To avoid that, we use waitqueue > + * for cgroup's rmdir. CGRP_WAIT_ON_RMDIR is for synchronizing rmdir > + * and subsystem's reference count handling. Please see css_get/put > + * and css_tryget() and cgroup_wakeup_rmdir_waiter() implementation. > + */ > + set_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags); > + > + /* > * Call pre_destroy handlers of subsys. Notify subsystems > * that rmdir() request comes. > */ > ret = cgroup_call_pre_destroy(cgrp); > - if (ret) > + if (ret) { > + clear_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags); > return ret; > + } > > mutex_lock(&cgroup_mutex); > parent = cgrp->parent; > if (atomic_read(&cgrp->count) || !list_empty(&cgrp->children)) { > + clear_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags); > mutex_unlock(&cgroup_mutex); > return -EBUSY; > } > - /* > - * css_put/get is provided for subsys to grab refcnt to css. In typical > - * case, subsystem has no reference after pre_destroy(). But, under > - * hierarchy management, some *temporal* refcnt can be hold. > - * To avoid returning -EBUSY to a user, waitqueue is used. If subsys > - * is really busy, it should return -EBUSY at pre_destroy(). wake_up > - * is called when css_put() is called and refcnt goes down to 0. > - */ > - set_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags); > prepare_to_wait(&cgroup_rmdir_waitq, &wait, TASK_INTERRUPTIBLE); > - > if (!cgroup_clear_css_refs(cgrp)) { > mutex_unlock(&cgroup_mutex); > - schedule(); > + /* > + * Because someone may call cgroup_wakeup_rmdir_waiter() before > + * prepare_to_wait(), we need to check this flag. > + */ > + if (test_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags)) > + schedule(); > finish_wait(&cgroup_rmdir_waitq, &wait); > clear_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags); > if (signal_pending(current)) > @@ -3294,7 +3315,7 @@ void __css_put(struct cgroup_subsys_stat > set_bit(CGRP_RELEASABLE, &cgrp->flags); > check_for_release(cgrp); > } > - cgroup_wakeup_rmdir_waiters(cgrp); > + cgroup_wakeup_rmdir_waiter(cgrp); > } > rcu_read_unlock(); > } > Index: mmotm-2.6.31-Jun25/mm/memcontrol.c > =================================================================== > --- mmotm-2.6.31-Jun25.orig/mm/memcontrol.c > +++ mmotm-2.6.31-Jun25/mm/memcontrol.c > @@ -1234,6 +1234,12 @@ static int mem_cgroup_move_account(struc > ret = 0; > out: > unlock_page_cgroup(pc); > + /* > + * We charges against "to" which may not have any tasks. Then, "to" > + * can be under rmdir(). But in current implementation, caller of > + * this function is just force_empty() and it's garanteed that > + * "to" is never removed. So, we don't check rmdir status here. > + */ > return ret; > } > > @@ -1455,6 +1461,7 @@ __mem_cgroup_commit_charge_swapin(struct > return; > if (!ptr) > return; > + cgroup_exclude_rmdir(&ptr->css); > pc = lookup_page_cgroup(page); > mem_cgroup_lru_del_before_commit_swapcache(page); > __mem_cgroup_commit_charge(ptr, pc, ctype); > @@ -1484,8 +1491,12 @@ __mem_cgroup_commit_charge_swapin(struct > } > rcu_read_unlock(); > } > - /* add this page(page_cgroup) to the LRU we want. */ > - > + /* > + * At swapin, we may charge account against cgroup which has no tasks. > + * So, rmdir()->pre_destroy() can be called while we do this charge. > + * In that case, we need to call pre_destroy() again. check it here. > + */ > + cgroup_release_rmdir(&ptr->css); > } > > void mem_cgroup_commit_charge_swapin(struct page *page, struct mem_cgroup *ptr) > @@ -1691,7 +1702,7 @@ void mem_cgroup_end_migration(struct mem > > if (!mem) > return; > - > + cgroup_exclude_rmdir(&mem->css); > /* at migration success, oldpage->mapping is NULL. */ > if (oldpage->mapping) { > target = oldpage; > @@ -1731,6 +1742,12 @@ void mem_cgroup_end_migration(struct mem > */ > if (ctype == MEM_CGROUP_CHARGE_TYPE_MAPPED) > mem_cgroup_uncharge_page(target); > + /* > + * At migration, we may charge account against cgroup which has no tasks > + * So, rmdir()->pre_destroy() can be called while we do this charge. > + * In that case, we need to call pre_destroy() again. check it here. > + */ > + cgroup_release_rmdir(&mem->css); > } > > /* > -- Balbir -- 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/