From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753335AbZGAP5S (ORCPT ); Wed, 1 Jul 2009 11:57:18 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752164AbZGAP5K (ORCPT ); Wed, 1 Jul 2009 11:57:10 -0400 Received: from smtp-out.google.com ([216.239.33.17]:5293 "EHLO smtp-out.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750896AbZGAP5J convert rfc822-to-8bit (ORCPT ); Wed, 1 Jul 2009 11:57:09 -0400 DomainKey-Signature: a=rsa-sha1; s=beta; d=google.com; c=nofws; q=dns; h=mime-version:in-reply-to:references:date:message-id:subject:from:to: cc:content-type:content-transfer-encoding:x-system-of-record; b=iXaRjGDZFxfK1SCa1sS3aB0x0mB5ShJTaYUlU9xMfrx6aDfwmKdh5pbjOeOrTNNiG R8ympcUKAPIlLQ2hKOkbg== MIME-Version: 1.0 In-Reply-To: <20090701104747.afdcc6c7.kamezawa.hiroyu@jp.fujitsu.com> References: <20090630180109.f137c10e.kamezawa.hiroyu@jp.fujitsu.com> <20090701104747.afdcc6c7.kamezawa.hiroyu@jp.fujitsu.com> Date: Wed, 1 Jul 2009 08:57:03 -0700 Message-ID: <6599ad830907010857r7fae2215r2e8aadb3003dcc4d@mail.gmail.com> Subject: Re: [PATCH] memcg: fix cgroup rmdir hang v4 From: Paul Menage To: KAMEZAWA Hiroyuki Cc: "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , "balbir@linux.vnet.ibm.com" , "nishimura@mxp.nes.nec.co.jp" Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT X-System-Of-Record: true Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jun 30, 2009 at 6:47 PM, KAMEZAWA Hiroyuki wrote: > 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. > >  - 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 Reviewed-by: Paul Menage Looks great, thanks. Paul > --- >  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) >  { > -       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); >  } > >  /* > >