Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755895AbZFVJi4 (ORCPT ); Mon, 22 Jun 2009 05:38:56 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752550AbZFVJir (ORCPT ); Mon, 22 Jun 2009 05:38:47 -0400 Received: from fgwmail5.fujitsu.co.jp ([192.51.44.35]:59029 "EHLO fgwmail5.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750765AbZFVJiq (ORCPT ); Mon, 22 Jun 2009 05:38:46 -0400 Date: Mon, 22 Jun 2009 18:37:07 +0900 From: KAMEZAWA Hiroyuki To: "linux-mm@kvack.org" Cc: "linux-kernel@vger.kernel.org" , "balbir@linux.vnet.ibm.com" , "linux-kernel@vger.kernel.org" , "nishimura@mxp.nes.nec.co.jp" , "menage@google.com" Subject: [RFC][PATCH] cgroup: fix permanent wait in rmdir Message-Id: <20090622183707.dd9e665b.kamezawa.hiroyu@jp.fujitsu.com> Organization: FUJITSU Co. LTD. X-Mailer: Sylpheed 2.5.0 (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: 7692 Lines: 215 previous discussion was this => http://marc.info/?t=124478543600001&r=1&w=2 I think this is a minimum fix (in code size and behavior) and because we can take a BIG LOCK, this kind of check is necessary, anyway. Any comments are welcome. == 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 before sleeping and export CGRP_WAIT_ON_RMDIR flag to subsys. Note: another solution will be adding "rmdir state" to subsys. But it will be much complicated than this do-enough-check solution. Reported-by: Daisuke Nishimura Signed-off-by: KAMEZAWA Hiroyuki --- Documentation/cgroups/cgroups.txt | 11 +++++++++++ include/linux/cgroup.h | 9 +++++++++ kernel/cgroup.c | 25 +++++++++++++++++++++---- mm/memcontrol.c | 29 ++++++++++++++++++++++++++--- 4 files changed, 67 insertions(+), 7 deletions(-) Index: linux-2.6.30-git18/include/linux/cgroup.h =================================================================== --- linux-2.6.30-git18.orig/include/linux/cgroup.h +++ linux-2.6.30-git18/include/linux/cgroup.h @@ -192,6 +192,14 @@ struct cgroup { struct rcu_head rcu_head; }; +void __cgroup_wakeup_rmdir_waiters(void); +static inline void cgroup_wakeup_rmdir_waiters(const struct cgroup *cgrp) +{ + if (unlikely(test_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags))) + __cgroup_wakeup_rmdir_waiters(); +} + + /* * A css_set is a structure holding pointers to a set of * cgroup_subsys_state objects. This saves space in the task struct @@ -374,6 +382,7 @@ 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: linux-2.6.30-git18/kernel/cgroup.c =================================================================== --- linux-2.6.30-git18.orig/kernel/cgroup.c +++ linux-2.6.30-git18/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) { @@ -738,10 +755,9 @@ static void cgroup_d_remove_dir(struct d */ DECLARE_WAIT_QUEUE_HEAD(cgroup_rmdir_waitq); -static void cgroup_wakeup_rmdir_waiters(const struct cgroup *cgrp) +void __cgroup_wakeup_rmdir_waiters(void) { - if (unlikely(test_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags))) - wake_up_all(&cgroup_rmdir_waitq); + wake_up_all(&cgroup_rmdir_waitq); } static int rebind_subsystems(struct cgroupfs_root *root, @@ -2722,7 +2738,8 @@ 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: linux-2.6.30-git18/mm/memcontrol.c =================================================================== --- linux-2.6.30-git18.orig/mm/memcontrol.c +++ linux-2.6.30-git18/mm/memcontrol.c @@ -179,7 +179,6 @@ struct mem_cgroup { /* set when res.limit == memsw.limit */ bool memsw_is_minimum; - /* * statistics. This must be placed at the end of memcg. */ @@ -1428,6 +1427,9 @@ __mem_cgroup_commit_charge_swapin(struct return; if (!ptr) return; + /* We access ptr->css.cgroup later. keep 1 refcnt here. */ + css_get(&ptr->css); + pc = lookup_page_cgroup(page); mem_cgroup_lru_del_before_commit_swapcache(page); __mem_cgroup_commit_charge(ptr, pc, ctype); @@ -1457,8 +1459,16 @@ __mem_cgroup_commit_charge_swapin(struct } rcu_read_unlock(); } - /* add this page(page_cgroup) to the LRU we want. */ - + /* + * At swapin, "ptr" is got from swap_cgroup and not from task. Then, + * this ptr can be under rmdir(). Under race with rmdir(), we may + * charge against cgroup which a thread is waiting for restart rmdir(). + * It can be waken up when css's refcnt goes to 0 but we charged... + * Because we can't do css_get()->charge in atomic, at swapin, we have + * to check there is no waiter for rmdir. + */ + cgroup_wakeup_rmdir_waiters(ptr->css.cgroup); + css_put(&ptr->css); } void mem_cgroup_commit_charge_swapin(struct page *page, struct mem_cgroup *ptr) @@ -2556,6 +2566,7 @@ mem_cgroup_create(struct cgroup_subsys * if (parent) mem->swappiness = get_swappiness(parent); + atomic_set(&mem->refcnt, 1); return &mem->css; free_out: @@ -2571,6 +2582,17 @@ 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(&memcg->res, RES_USAGE)) + return 1; + return 0; +} + + static void mem_cgroup_destroy(struct cgroup_subsys *ss, struct cgroup *cont) { @@ -2610,6 +2632,7 @@ 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: linux-2.6.30-git18/Documentation/cgroups/cgroups.txt =================================================================== --- linux-2.6.30-git18.orig/Documentation/cgroups/cgroups.txt +++ linux-2.6.30-git18/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 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/