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cgroup: simplify dynamic cftype addition and removal 

Dynamic cftype addition and removal using cgroup_add/rm_cftypes()
respectively has been quite hairy due to vfs i_mutex.  As i_mutex
nests outside cgroup_mutex, cgroup_mutex has to be released and
regrabbed on each iteration through the hierarchy complicating the
process.  Now that i_mutex is no longer in play, it can be simplified.

* Just holding cgroup_tree_mutex is enough.  No need to meddle with
  cgroup_mutex.

* No reason to play the unlock - relock - check serial_nr dancing.
  Everything can be atomically while holding cgroup_tree_mutex.

* cgroup_cfts_prepare() is replaced with direct locking of
  cgroup_tree_mutex.

* cgroup_cfts_commit() no longer fiddles with locking.  It just
  applies the cftypes change to the existing cgroups in the hierarchy.
  Renamed to cgroup_cfts_apply().

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
This commit is contained in:
Tejun Heo 2014-02-12 09:29:49 -05:00
parent 0adb070426
commit 21a2d3430b
1 changed files with 32 additions and 55 deletions
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87
kernel/cgroup.c
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@ -2305,46 +2305,19 @@ static int cgroup_addrm_files(struct cgroup *cgrp, struct cftype cfts[],
return 0;
}
static void cgroup_cfts_prepare(void)
__acquires(&cgroup_mutex)
{
/*
* Thanks to the entanglement with vfs inode locking, we can't walk
* the existing cgroups under cgroup_mutex and create files.
* Instead, we use css_for_each_descendant_pre() and drop RCU read
* lock before calling cgroup_addrm_files().
*/
mutex_lock(&cgroup_tree_mutex);
mutex_lock(&cgroup_mutex);
}
static int cgroup_cfts_commit(struct cftype *cfts, bool is_add)
__releases(&cgroup_mutex)
static int cgroup_apply_cftypes(struct cftype *cfts, bool is_add)
{
LIST_HEAD(pending);
struct cgroup_subsys *ss = cfts[0].ss;
struct cgroup *root = &ss->root->top_cgroup;
struct cgroup *prev = NULL;
struct cgroup_subsys_state *css;
u64 update_before;
int ret = 0;
mutex_unlock(&cgroup_mutex);
lockdep_assert_held(&cgroup_tree_mutex);
/* %NULL @cfts indicates abort and don't bother if @ss isn't attached */
if (!cfts || ss->root == &cgroup_dummy_root) {
mutex_unlock(&cgroup_tree_mutex);
/* don't bother if @ss isn't attached */
if (ss->root == &cgroup_dummy_root)
return 0;
}
cgroup_get_root(ss->root);
/*
* All cgroups which are created after we drop cgroup_mutex will
* have the updated set of files, so we only need to update the
* cgroups created before the current @cgroup_serial_nr_next.
*/
update_before = cgroup_serial_nr_next;
/* add/rm files for all cgroups created before */
css_for_each_descendant_pre(css, cgroup_css(root, ss)) {
@ -2353,22 +2326,13 @@ static int cgroup_cfts_commit(struct cftype *cfts, bool is_add)
if (cgroup_is_dead(cgrp))
continue;
cgroup_get(cgrp);
if (prev)
cgroup_put(prev);
prev = cgrp;
if (cgrp->serial_nr < update_before && !cgroup_is_dead(cgrp)) {
ret = cgroup_addrm_files(cgrp, cfts, is_add);
if (is_add)
kernfs_activate(cgrp->kn);
}
ret = cgroup_addrm_files(cgrp, cfts, is_add);
if (ret)
break;
}
mutex_unlock(&cgroup_tree_mutex);
cgroup_put(prev);
cgroup_put_root(ss->root);
if (is_add && !ret)
kernfs_activate(root->kn);
return ret;
}
@ -2419,6 +2383,19 @@ static int cgroup_init_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
return 0;
}
static int cgroup_rm_cftypes_locked(struct cftype *cfts)
{
lockdep_assert_held(&cgroup_tree_mutex);
if (!cfts || !cfts[0].ss)
return -ENOENT;
list_del(&cfts->node);
cgroup_apply_cftypes(cfts, false);
cgroup_exit_cftypes(cfts);
return 0;
}
/**
* cgroup_rm_cftypes - remove an array of cftypes from a subsystem
* @cfts: zero-length name terminated array of cftypes
@ -2432,15 +2409,12 @@ static int cgroup_init_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
*/
int cgroup_rm_cftypes(struct cftype *cfts)
{
if (!cfts || !cfts[0].ss)
return -ENOENT;
int ret;
cgroup_cfts_prepare();
list_del(&cfts->node);
cgroup_cfts_commit(cfts, false);
cgroup_exit_cftypes(cfts);
return 0;
mutex_lock(&cgroup_tree_mutex);
ret = cgroup_rm_cftypes_locked(cfts);
mutex_unlock(&cgroup_tree_mutex);
return ret;
}
/**
@ -2465,11 +2439,14 @@ int cgroup_add_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
if (ret)
return ret;
cgroup_cfts_prepare();
mutex_lock(&cgroup_tree_mutex);
list_add_tail(&cfts->node, &ss->cfts);
ret = cgroup_cfts_commit(cfts, true);
ret = cgroup_apply_cftypes(cfts, true);
if (ret)
cgroup_rm_cftypes(cfts);
cgroup_rm_cftypes_locked(cfts);
mutex_unlock(&cgroup_tree_mutex);
return ret;
}
EXPORT_SYMBOL_GPL(cgroup_add_cftypes);