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Message-Id: <20090626141020.849a081e.kamezawa.hiroyu@jp.fujitsu.com>
Date: Fri, 26 Jun 2009 14:10:20 +0900
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc: "linux-mm@...ck.org" <linux-mm@...ck.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"nishimura@....nes.nec.co.jp" <nishimura@....nes.nec.co.jp>,
"balbir@...ux.vnet.ibm.com" <balbir@...ux.vnet.ibm.com>,
"lizf@...fujitsu.com" <lizf@...fujitsu.com>,
"menage@...gle.com" <menage@...gle.com>,
"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>
Subject: [PATCH] memcg: cgroup fix rmdir hang
I hope this will be a final bullet..
I myself think this one is enough simple and good.
I'm sorry that we need test again.
==
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
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 v2->v3:
- removed retry_rmdir() callback.
- make use of CGRP_WAIT_ON_RMDIR flag more.
Reported-by: Daisuke Nishimura <nishimura@....nes.nec.co.jp>
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
---
include/linux/cgroup.h | 13 +++++++++++++
kernel/cgroup.c | 38 ++++++++++++++++++++++----------------
mm/memcontrol.c | 25 +++++++++++++++++++++++--
3 files changed, 58 insertions(+), 18 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 +366,19 @@ int cgroup_task_count(const struct cgrou
int cgroup_is_descendant(const struct cgroup *cgrp, struct task_struct *task);
/*
+ * Allow to use CGRP_WAIT_ON_RMDIR flag to check race with rmdir() for subsys.
+ * Subsys can call this function if it's necessary to call pre_destroy() again
+ * because it adds not-temporary refs to css after or while pre_destroy().
+ * The caller of this function should use css_tryget(), too.
+ */
+void __cgroup_wakeup_rmdir_waiters(void);
+static inline void cgroup_wakeup_rmdir_waiters(struct cgroup *cgrp)
+{
+ if (unlikely(test_and_clear_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags)))
+ __cgroup_wakeup_rmdir_waiters();
+}
+
+/*
* 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
@@ -734,14 +734,13 @@ 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)
+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,
@@ -2696,33 +2695,40 @@ again:
mutex_unlock(&cgroup_mutex);
/*
+ * 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.
+ * And this WAIT_ON_RMDIR flag is cleared when subsys detect a race
+ * condition under pre_destroy()->rmdir. If flag is cleared, we need
+ * to call pre_destroy(), again.
+ */
+ 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();
+ 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))
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;
+ css_get(&ptr->css);
pc = lookup_page_cgroup(page);
mem_cgroup_lru_del_before_commit_swapcache(page);
__mem_cgroup_commit_charge(ptr, pc, ctype);
@@ -1484,7 +1491,13 @@ __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_wakeup_rmdir_waiters(ptr->css.cgroup);
+ css_put(&ptr->css);
}
@@ -1691,7 +1704,7 @@ void mem_cgroup_end_migration(struct mem
if (!mem)
return;
-
+ css_get(&mem->css);
/* at migration success, oldpage->mapping is NULL. */
if (oldpage->mapping) {
target = oldpage;
@@ -1731,6 +1744,14 @@ 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_wakeup_rmdir_waiters(mem->css.cgroup);
+ css_put(&mem->css);
+
}
/*
--
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