Commit 21a2d343 authored by Tejun Heo's avatar Tejun Heo

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: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarLi Zefan <lizefan@huawei.com>
parent 0adb0704
...@@ -2305,46 +2305,19 @@ static int cgroup_addrm_files(struct cgroup *cgrp, struct cftype cfts[], ...@@ -2305,46 +2305,19 @@ static int cgroup_addrm_files(struct cgroup *cgrp, struct cftype cfts[],
return 0; return 0;
} }
static void cgroup_cfts_prepare(void) static int cgroup_apply_cftypes(struct cftype *cfts, bool is_add)
__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)
{ {
LIST_HEAD(pending); LIST_HEAD(pending);
struct cgroup_subsys *ss = cfts[0].ss; struct cgroup_subsys *ss = cfts[0].ss;
struct cgroup *root = &ss->root->top_cgroup; struct cgroup *root = &ss->root->top_cgroup;
struct cgroup *prev = NULL;
struct cgroup_subsys_state *css; struct cgroup_subsys_state *css;
u64 update_before;
int ret = 0; 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 */ /* don't bother if @ss isn't attached */
if (!cfts || ss->root == &cgroup_dummy_root) { if (ss->root == &cgroup_dummy_root)
mutex_unlock(&cgroup_tree_mutex);
return 0; 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 */ /* add/rm files for all cgroups created before */
css_for_each_descendant_pre(css, cgroup_css(root, ss)) { 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) ...@@ -2353,22 +2326,13 @@ static int cgroup_cfts_commit(struct cftype *cfts, bool is_add)
if (cgroup_is_dead(cgrp)) if (cgroup_is_dead(cgrp))
continue; continue;
cgroup_get(cgrp); ret = cgroup_addrm_files(cgrp, cfts, is_add);
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);
}
if (ret) if (ret)
break; break;
} }
mutex_unlock(&cgroup_tree_mutex);
cgroup_put(prev); if (is_add && !ret)
cgroup_put_root(ss->root); kernfs_activate(root->kn);
return ret; return ret;
} }
...@@ -2419,6 +2383,19 @@ static int cgroup_init_cftypes(struct cgroup_subsys *ss, struct cftype *cfts) ...@@ -2419,6 +2383,19 @@ static int cgroup_init_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
return 0; 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 * cgroup_rm_cftypes - remove an array of cftypes from a subsystem
* @cfts: zero-length name terminated array of cftypes * @cfts: zero-length name terminated array of cftypes
...@@ -2432,15 +2409,12 @@ static int cgroup_init_cftypes(struct cgroup_subsys *ss, struct cftype *cfts) ...@@ -2432,15 +2409,12 @@ static int cgroup_init_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
*/ */
int cgroup_rm_cftypes(struct cftype *cfts) int cgroup_rm_cftypes(struct cftype *cfts)
{ {
if (!cfts || !cfts[0].ss) int ret;
return -ENOENT;
cgroup_cfts_prepare();
list_del(&cfts->node);
cgroup_cfts_commit(cfts, false);
cgroup_exit_cftypes(cfts); mutex_lock(&cgroup_tree_mutex);
return 0; 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) ...@@ -2465,11 +2439,14 @@ int cgroup_add_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
if (ret) if (ret)
return ret; return ret;
cgroup_cfts_prepare(); mutex_lock(&cgroup_tree_mutex);
list_add_tail(&cfts->node, &ss->cfts); list_add_tail(&cfts->node, &ss->cfts);
ret = cgroup_cfts_commit(cfts, true); ret = cgroup_apply_cftypes(cfts, true);
if (ret) if (ret)
cgroup_rm_cftypes(cfts); cgroup_rm_cftypes_locked(cfts);
mutex_unlock(&cgroup_tree_mutex);
return ret; return ret;
} }
EXPORT_SYMBOL_GPL(cgroup_add_cftypes); EXPORT_SYMBOL_GPL(cgroup_add_cftypes);
......
Markdown is supported
0%
or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment