>From 705da98c48f39ebe565439353a5b35a0bab08b23 Mon Sep 17 00:00:00 2001
From: Tejun Heo <tj@xxxxxxxxxx>
Date: Fri, 28 Jun 2013 17:07:30 -0700
Currently, creating and removing cgroup files in the root directory
are handled separately from the actual subsystem binding and unbinding
which happens in rebind_subsystems(). Also, rebind_subsystems() users
aren't handling file creation errors properly. Let's integrate
top_cgroup file handling into rebind_subsystems() so that it's simpler
to use and everyone handles file creation errors correctly.
* On a successful return, rebind_subsystems() is guaranteed to have
created all files of the new subsystems and deleted the ones
belonging to the removed subsystems. After a failure, no file is
created or removed.
* cgroup_remount() no longer needs to make explicit populate/clear
calls as it's all handled by rebind_subsystems(), and it gets proper
error handling automatically.
* cgroup_mount() has been updated such that the root dentry and cgroup
are linked before rebind_subsystems(). Also, the init_cred dancing
and base file handling are moved right above rebind_subsystems()
call and proper error handling for the base files is added. While
at it, add a comment explaining what's going on with the cred thing.
* cgroup_kill_sb() calls rebind_subsystems() to unbind all subsystems
which now implies removing all subsystem files which requires the
directory's i_mutex. Grab it. This means that files on the root
cgroup are removed earlier - they used to be deleted from generic
super_block cleanup from vfs. This doesn't lead to any functional
difference and it's cleaner to do the clean up explicitly for all
files.
Combined with the previous changes, this makes all cgroup file
creation errors handled correctly.
v2: Added comment on init_cred.
v3: Li spotted that cgroup_mount() wasn't freeing tmp_links after base
file addition failure. Fix it by adding free_tmp_links error
handling label.
v4: v3 introduced build bugs which got noticed by Fengguang's awesome
kbuild test robot. Fixed, and shame on me.
Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Acked-by: Li Zefan <lizefan@xxxxxxxxxx>
Cc: Fengguang Wu <fengguang.wu@xxxxxxxxx>
---
I introduced a build bug on v3 and failed to notice it. I probably
did build testing without the patch applied. The tree has been
updated.
Thanks.
kernel/cgroup.c | 73 +++++++++++++++++++++++++++++++-------------------------
1 file changed, 41 insertions(+), 32 deletions(-)
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1003,7 +1003,7 @@ static int rebind_subsystems(struct cgro
{
struct cgroup *cgrp = &root->top_cgroup;
struct cgroup_subsys *ss;
- int i;
+ int i, ret;
BUG_ON(!mutex_is_locked(&cgroup_mutex));
BUG_ON(!mutex_is_locked(&cgroup_root_mutex));
@@ -1028,7 +1028,16 @@ static int rebind_subsystems(struct cgro
if (root->number_of_cgroups > 1)
return -EBUSY;
- /* Process each subsystem */
+ ret = cgroup_populate_dir(cgrp, added_mask);
+ if (ret)
+ return ret;
+
+ /*
+ * Nothing can fail from this point on. Remove files for the
+ * removed subsystems and rebind each subsystem.
+ */
+ cgroup_clear_dir(cgrp, removed_mask);
+
for_each_subsys(ss, i) {
unsigned long bit = 1UL << i;
@@ -1364,22 +1373,9 @@ static int cgroup_remount(struct super_b
goto out_unlock;
}
- /*
- * Clear out the files of subsystems that should be removed, do
- * this before rebind_subsystems, since rebind_subsystems may
- * change this hierarchy's subsys_list.
- */
- cgroup_clear_dir(cgrp, removed_mask);
-
ret = rebind_subsystems(root, added_mask, removed_mask);
- if (ret) {
- /* rebind_subsystems failed, re-populate the removed files */
- cgroup_populate_dir(cgrp, removed_mask);
+ if (ret)
goto out_unlock;
- }
-
- /* re-populate subsystem files */
- cgroup_populate_dir(cgrp, added_mask);
if (opts.release_agent)
strcpy(root->release_agent_path, opts.release_agent);
@@ -1578,7 +1574,9 @@ static struct dentry *cgroup_mount(struc
int ret = 0;
struct super_block *sb;
struct cgroupfs_root *new_root;
+ struct list_head tmp_links;
struct inode *inode;
+ const struct cred *cred;
/* First find the desired set of subsystems */
mutex_lock(&cgroup_mutex);
@@ -1610,10 +1608,8 @@ static struct dentry *cgroup_mount(struc
BUG_ON(!root);
if (root == opts.new_root) {
/* We used the new root structure, so this is a new hierarchy */
- struct list_head tmp_links;
struct cgroup *root_cgrp = &root->top_cgroup;
struct cgroupfs_root *existing_root;
- const struct cred *cred;
int i;
struct css_set *cset;
@@ -1651,26 +1647,37 @@ static struct dentry *cgroup_mount(struc
if (ret)
goto unlock_drop;
+ sb->s_root->d_fsdata = root_cgrp;
+ root_cgrp->dentry = sb->s_root;
+
+ /*
+ * We're inside get_sb() and will call lookup_one_len() to
+ * create the root files, which doesn't work if SELinux is
+ * in use. The following cred dancing somehow works around
+ * it. See 2ce9738ba ("cgroupfs: use init_cred when
+ * populating new cgroupfs mount") for more details.
+ */
+ cred = override_creds(&init_cred);
+
+ ret = cgroup_addrm_files(root_cgrp, NULL, cgroup_base_files, true);
+ if (ret)
+ goto rm_base_files;
+
ret = rebind_subsystems(root, root->subsys_mask, 0);
- if (ret == -EBUSY) {
- free_cgrp_cset_links(&tmp_links);
- goto unlock_drop;
- }
+ if (ret)
+ goto rm_base_files;
+
+ revert_creds(cred);
+
/*
* There must be no failure case after here, since rebinding
* takes care of subsystems' refcounts, which are explicitly
* dropped in the failure exit path.
*/
- /* EBUSY should be the only error here */
- BUG_ON(ret);
-
list_add(&root->root_list, &cgroup_roots);
cgroup_root_count++;
- sb->s_root->d_fsdata = root_cgrp;
- root->top_cgroup.dentry = sb->s_root;
-
/* Link the top cgroup in this hierarchy into all
* the css_set objects */
write_lock(&css_set_lock);
@@ -1683,10 +1690,6 @@ static struct dentry *cgroup_mount(struc
BUG_ON(!list_empty(&root_cgrp->children));
BUG_ON(root->number_of_cgroups != 1);
- cred = override_creds(&init_cred);
- cgroup_addrm_files(root_cgrp, NULL, cgroup_base_files, true);
- cgroup_populate_dir(root_cgrp, root->subsys_mask);
- revert_creds(cred);
mutex_unlock(&cgroup_root_mutex);
mutex_unlock(&cgroup_mutex);
mutex_unlock(&inode->i_mutex);
@@ -1715,6 +1718,10 @@ static struct dentry *cgroup_mount(struc
kfree(opts.name);
return dget(sb->s_root);
+ rm_base_files:
+ free_cgrp_cset_links(&tmp_links);
+ cgroup_addrm_files(&root->top_cgroup, NULL, cgroup_base_files, false);
+ revert_creds(cred);
unlock_drop:
cgroup_exit_root_id(root);
mutex_unlock(&cgroup_root_mutex);
@@ -1741,6 +1748,7 @@ static void cgroup_kill_sb(struct super_
BUG_ON(root->number_of_cgroups != 1);
BUG_ON(!list_empty(&cgrp->children));
+ mutex_lock(&cgrp->dentry->d_inode->i_mutex);
mutex_lock(&cgroup_mutex);
mutex_lock(&cgroup_root_mutex);
@@ -1773,6 +1781,7 @@ static void cgroup_kill_sb(struct super_
mutex_unlock(&cgroup_root_mutex);
mutex_unlock(&cgroup_mutex);
+ mutex_unlock(&cgrp->dentry->d_inode->i_mutex);
simple_xattrs_free(&cgrp->xattrs);
_______________________________________________
Containers mailing list
Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx
https://lists.linuxfoundation.org/mailman/listinfo/containers
