lkml.org 
[lkml]   [2014]   [Feb]   [8]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH 4/8] cgroup: simplify dynamic cftype addition and removal
Date
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>
---
kernel/cgroup.c | 87 +++++++++++++++++++++------------------------------------
1 file changed, 32 insertions(+), 55 deletions(-)

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index a3ade20..6da820d 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -2303,46 +2303,19 @@ 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)) {
@@ -2351,22 +2324,13 @@ 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;
}

@@ -2417,6 +2381,19 @@ 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
@@ -2430,15 +2407,12 @@ 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;
-
- cgroup_cfts_prepare();
- list_del(&cfts->node);
- cgroup_cfts_commit(cfts, false);
+ int ret;

- cgroup_exit_cftypes(cfts);
- return 0;
+ mutex_lock(&cgroup_tree_mutex);
+ ret = cgroup_rm_cftypes_locked(cfts);
+ mutex_unlock(&cgroup_tree_mutex);
+ return ret;
}

/**
@@ -2463,11 +2437,14 @@ 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);
--
1.8.5.3


\
 
 \ /
  Last update: 2014-02-08 18:21    [W:0.072 / U:0.064 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site