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Subject[PATCH 2/2] cgroup: exlclude release rmdir
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

Paul Menage pointed out that css_get()/put() only for avoiding race with
rmdir() is complicated and these should be treated as it is for.

This adds
- cgroup_exclude_rmdir() ....prevent rmdir() for a while.
- cgroup_release_rmdir() ....rerun rmdir() if necessary.
And hides cgroup_wakeup_rmdir_waiter() into kernel/cgroup.c, again.
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

---
include/linux/cgroup.h | 21 +++++++++++----------
kernel/cgroup.c | 17 +++++++++++++++--
mm/memcontrol.c | 12 ++++--------
3 files changed, 30 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
@@ -366,17 +366,18 @@ 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.
+ * 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_wakeup_rmdir_waiters(void);
-static inline void cgroup_wakeup_rmdir_waiter(struct cgroup *cgrp)
-{
- if (unlikely(test_and_clear_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags)))
- __cgroup_wakeup_rmdir_waiters();
-}
+
+void cgroup_exclude_rmdir(struct cgroup_subsys_state *css);
+void cgroup_release_rmdir(struct cgroup_subsys_state *css);

/*
* Control Group subsystem type.
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
@@ -738,11 +738,24 @@ static void cgroup_d_remove_dir(struct d
*/
DECLARE_WAIT_QUEUE_HEAD(cgroup_rmdir_waitq);

-void __cgroup_wakeup_rmdir_waiters(void)
+static void cgroup_wakeup_rmdir_waiter(struct cgroup *cgrp)
{
- wake_up_all(&cgroup_rmdir_waitq);
+ 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)
{
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
@@ -1461,7 +1461,7 @@ __mem_cgroup_commit_charge_swapin(struct
return;
if (!ptr)
return;
- css_get(&ptr->css);
+ 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);
@@ -1496,9 +1496,7 @@ __mem_cgroup_commit_charge_swapin(struct
* 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_waiter(ptr->css.cgroup);
- css_put(&ptr->css);
-
+ cgroup_release_rmdir(&ptr->css);
}

void mem_cgroup_commit_charge_swapin(struct page *page, struct mem_cgroup *ptr)
@@ -1704,7 +1702,7 @@ void mem_cgroup_end_migration(struct mem

if (!mem)
return;
- css_get(&mem->css);
+ cgroup_exclude_rmdir(&mem->css);
/* at migration success, oldpage->mapping is NULL. */
if (oldpage->mapping) {
target = oldpage;
@@ -1749,9 +1747,7 @@ void mem_cgroup_end_migration(struct mem
* 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_waiter(mem->css.cgroup);
- css_put(&mem->css);
-
+ cgroup_release_rmdir(&mem->css);
}

/*


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