Messages in this thread Patch in this message | | | Date | Tue, 23 Jun 2009 16:08:54 +0900 | From | KAMEZAWA Hiroyuki <> | Subject | [PATCH 1/2] memcg: cgroup fix rmdir hang |
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From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
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 <nishimura@mxp.nes.nec.co.jp> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> --- 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)
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