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cgroup: remove CGRP_RELEASABLE flag

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We call put_css_set() after setting CGRP_RELEASABLE flag in
cgroup_task_migrate(), but in other places we call it without setting
the flag. I don't see the necessity of this flag.

Moreover once the flag is set, it will never be cleared, unless writing
to the notify_on_release control file, so it can be quite confusing
if we look at the output of debug.releasable.

  # mount -t cgroup -o debug xxx /cgroup
  # mkdir /cgroup/child
  # cat /cgroup/child/debug.releasable
  0   <-- shows 0 though the cgroup is empty
  # echo $$ > /cgroup/child/tasks
  # cat /cgroup/child/debug.releasable
  0
  # echo $$ > /cgroup/tasks && echo $$ > /cgroup/child/tasks
  # cat /proc/child/debug.releasable
  1   <-- shows 1 though the cgroup is not empty

This patch removes the flag, and now debug.releasable shows if the
cgroup is empty or not.

Signed-off-by: Zefan Li <lizefan@huawei.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Zefan Li 2014-09-19 16:51:00 +08:00 committed by Tejun Heo
parent 4e2ba65068
commit a25eb52e81
2 changed files with 13 additions and 32 deletions
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5
include/linux/cgroup.h
View File

@ -161,11 +161,6 @@ static inline void css_put(struct cgroup_subsys_state *css)
/* bits in struct cgroup flags field */ /* bits in struct cgroup flags field */
enum { enum {
/*
* Control Group has previously had a child cgroup or a task,
* but no longer (only if CGRP_NOTIFY_ON_RELEASE is set)
*/
CGRP_RELEASABLE,
/* Control Group requires release notifications to userspace */ /* Control Group requires release notifications to userspace */
CGRP_NOTIFY_ON_RELEASE, CGRP_NOTIFY_ON_RELEASE,
/* /*

40
kernel/cgroup.c
View File

@ -329,14 +329,6 @@ bool cgroup_is_descendant(struct cgroup *cgrp, struct cgroup *ancestor)
return false; return false;
} }
static int cgroup_is_releasable(const struct cgroup *cgrp)
{
const int bits =
(1 << CGRP_RELEASABLE) |
(1 << CGRP_NOTIFY_ON_RELEASE);
return (cgrp->flags & bits) == bits;
}
static int notify_on_release(const struct cgroup *cgrp) static int notify_on_release(const struct cgroup *cgrp)
{ {
return test_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags); return test_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
@ -491,7 +483,7 @@ static unsigned long css_set_hash(struct cgroup_subsys_state *css[])
return key; return key;
} }
static void put_css_set_locked(struct css_set *cset, bool taskexit) static void put_css_set_locked(struct css_set *cset)
{ {
struct cgrp_cset_link *link, *tmp_link; struct cgrp_cset_link *link, *tmp_link;
struct cgroup_subsys *ss; struct cgroup_subsys *ss;
@ -517,11 +509,7 @@ static void put_css_set_locked(struct css_set *cset, bool taskexit)
/* @cgrp can't go away while we're holding css_set_rwsem */ /* @cgrp can't go away while we're holding css_set_rwsem */
if (list_empty(&cgrp->cset_links)) { if (list_empty(&cgrp->cset_links)) {
cgroup_update_populated(cgrp, false); cgroup_update_populated(cgrp, false);
if (notify_on_release(cgrp)) { check_for_release(cgrp);
if (taskexit)
set_bit(CGRP_RELEASABLE, &cgrp->flags);
check_for_release(cgrp);
}
} }
kfree(link); kfree(link);
@ -530,7 +518,7 @@ static void put_css_set_locked(struct css_set *cset, bool taskexit)
kfree_rcu(cset, rcu_head); kfree_rcu(cset, rcu_head);
} }
static void put_css_set(struct css_set *cset, bool taskexit) static void put_css_set(struct css_set *cset)
{ {
/* /*
* Ensure that the refcount doesn't hit zero while any readers * Ensure that the refcount doesn't hit zero while any readers
@ -541,7 +529,7 @@ static void put_css_set(struct css_set *cset, bool taskexit)
return; return;
down_write(&css_set_rwsem); down_write(&css_set_rwsem);
put_css_set_locked(cset, taskexit); put_css_set_locked(cset);
up_write(&css_set_rwsem); up_write(&css_set_rwsem);
} }
@ -2037,8 +2025,7 @@ static void cgroup_task_migrate(struct cgroup *old_cgrp,
* task. As trading it for new_cset is protected by cgroup_mutex, * task. As trading it for new_cset is protected by cgroup_mutex,
* we're safe to drop it here; it will be freed under RCU. * we're safe to drop it here; it will be freed under RCU.
*/ */
set_bit(CGRP_RELEASABLE, &old_cgrp->flags); put_css_set_locked(old_cset);
put_css_set_locked(old_cset, false);
} }
/** /**
@ -2059,7 +2046,7 @@ static void cgroup_migrate_finish(struct list_head *preloaded_csets)
cset->mg_src_cgrp = NULL; cset->mg_src_cgrp = NULL;
cset->mg_dst_cset = NULL; cset->mg_dst_cset = NULL;
list_del_init(&cset->mg_preload_node); list_del_init(&cset->mg_preload_node);
put_css_set_locked(cset, false); put_css_set_locked(cset);
} }
up_write(&css_set_rwsem); up_write(&css_set_rwsem);
} }
@ -2153,8 +2140,8 @@ static int cgroup_migrate_prepare_dst(struct cgroup *dst_cgrp,
if (src_cset == dst_cset) { if (src_cset == dst_cset) {
src_cset->mg_src_cgrp = NULL; src_cset->mg_src_cgrp = NULL;
list_del_init(&src_cset->mg_preload_node); list_del_init(&src_cset->mg_preload_node);
put_css_set(src_cset, false); put_css_set(src_cset);
put_css_set(dst_cset, false); put_css_set(dst_cset);
continue; continue;
} }
@ -2163,7 +2150,7 @@ static int cgroup_migrate_prepare_dst(struct cgroup *dst_cgrp,
if (list_empty(&dst_cset->mg_preload_node)) if (list_empty(&dst_cset->mg_preload_node))
list_add(&dst_cset->mg_preload_node, &csets); list_add(&dst_cset->mg_preload_node, &csets);
else else
put_css_set(dst_cset, false); put_css_set(dst_cset);
} }
list_splice_tail(&csets, preloaded_csets); list_splice_tail(&csets, preloaded_csets);
@ -4159,7 +4146,6 @@ static u64 cgroup_read_notify_on_release(struct cgroup_subsys_state *css,
static int cgroup_write_notify_on_release(struct cgroup_subsys_state *css, static int cgroup_write_notify_on_release(struct cgroup_subsys_state *css,
struct cftype *cft, u64 val) struct cftype *cft, u64 val)
{ {
clear_bit(CGRP_RELEASABLE, &css->cgroup->flags);
if (val) if (val)
set_bit(CGRP_NOTIFY_ON_RELEASE, &css->cgroup->flags); set_bit(CGRP_NOTIFY_ON_RELEASE, &css->cgroup->flags);
else else
@ -4806,7 +4792,6 @@ static int cgroup_destroy_locked(struct cgroup *cgrp)
*/ */
kernfs_remove(cgrp->kn); kernfs_remove(cgrp->kn);
set_bit(CGRP_RELEASABLE, &cgroup_parent(cgrp)->flags);
check_for_release(cgroup_parent(cgrp)); check_for_release(cgroup_parent(cgrp));
/* put the base reference */ /* put the base reference */
@ -5244,12 +5229,12 @@ void cgroup_exit(struct task_struct *tsk)
} }
if (put_cset) if (put_cset)
put_css_set(cset, true); put_css_set(cset);
} }
static void check_for_release(struct cgroup *cgrp) static void check_for_release(struct cgroup *cgrp)
{ {
if (cgroup_is_releasable(cgrp) && !cgroup_has_tasks(cgrp) && if (notify_on_release(cgrp) && !cgroup_has_tasks(cgrp) &&
!css_has_online_children(&cgrp->self) && !cgroup_is_dead(cgrp)) !css_has_online_children(&cgrp->self) && !cgroup_is_dead(cgrp))
schedule_work(&cgrp->release_agent_work); schedule_work(&cgrp->release_agent_work);
} }
@ -5496,7 +5481,8 @@ static int cgroup_css_links_read(struct seq_file *seq, void *v)
static u64 releasable_read(struct cgroup_subsys_state *css, struct cftype *cft) static u64 releasable_read(struct cgroup_subsys_state *css, struct cftype *cft)
{ {
return test_bit(CGRP_RELEASABLE, &css->cgroup->flags); return (!cgroup_has_tasks(css->cgroup) &&
!css_has_online_children(&css->cgroup->self));
} }
static struct cftype debug_files[] = { static struct cftype debug_files[] = {