cgroup curiously has two subsystem masks, ->subsys_mask and
->actual_subsys_mask. The latter only exists because the new target
subsys_mask is passed into rebind_subsystems() via @cgrp->subsys_mask.
rebind_subsystems() needs to know what the current mask is to decide
how to reach the target mask so ->actual_subsys_mask is used as the
temp location to remember the current state.
Adding a temporary field to a permanent data structure is rather silly
and can be misleading. Update rebind_subsystems() to take @added_mask
and @removed_mask instead and remove @cgrp->actual_subsys_mask.
This patch shouldn't introduce any behavior changes.
Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
---
include/linux/cgroup.h | 3 ---
kernel/cgroup.c | 22 ++++++++++++----------
2 files changed, 12 insertions(+), 13 deletions(-)
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 46a59d0..7d8c4ec 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -295,9 +295,6 @@ struct cgroupfs_root {
/* Unique id for this hierarchy. */
int hierarchy_id;
- /* The bitmask of subsystems currently attached to this hierarchy */
- unsigned long actual_subsys_mask;
-
/* A list running through the attached subsystems */
struct list_head subsys_list;
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index dbb4418..c3222a7 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -986,17 +986,14 @@ static void cgroup_d_remove_dir(struct dentry *dentry)
* returns an error, no reference counts are touched.
*/
static int rebind_subsystems(struct cgroupfs_root *root,
- unsigned long final_subsys_mask)
+ unsigned long added_mask, unsigned removed_mask)
{
- unsigned long added_mask, removed_mask;
struct cgroup *cgrp = &root->top_cgroup;
int i;
BUG_ON(!mutex_is_locked(&cgroup_mutex));
BUG_ON(!mutex_is_locked(&cgroup_root_mutex));
- removed_mask = root->actual_subsys_mask & ~final_subsys_mask;
- added_mask = final_subsys_mask & ~root->actual_subsys_mask;
/* Check that any added subsystems are currently free */
for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
unsigned long bit = 1UL << i;
@@ -1032,27 +1029,33 @@ static int rebind_subsystems(struct cgroupfs_root *root,
BUG_ON(cgrp->subsys[i]);
BUG_ON(!cgroup_dummy_top->subsys[i]);
BUG_ON(cgroup_dummy_top->subsys[i]->cgroup != cgroup_dummy_top);
+
cgrp->subsys[i] = cgroup_dummy_top->subsys[i];
cgrp->subsys[i]->cgroup = cgrp;
list_move(&ss->sibling, &root->subsys_list);
ss->root = root;
if (ss->bind)
ss->bind(cgrp);
+
/* refcount was already taken, and we're keeping it */
+ root->subsys_mask |= bit;
} else if (bit & removed_mask) {
/* We're removing this subsystem */
BUG_ON(ss == NULL);
BUG_ON(cgrp->subsys[i] != cgroup_dummy_top->subsys[i]);
BUG_ON(cgrp->subsys[i]->cgroup != cgrp);
+
if (ss->bind)
ss->bind(cgroup_dummy_top);
cgroup_dummy_top->subsys[i]->cgroup = cgroup_dummy_top;
cgrp->subsys[i] = NULL;
cgroup_subsys[i]->root = &cgroup_dummy_root;
list_move(&ss->sibling, &cgroup_dummy_root.subsys_list);
+
/* subsystem is now free - drop reference on module */
module_put(ss->module);
- } else if (bit & final_subsys_mask) {
+ root->subsys_mask &= ~bit;
+ } else if (bit & root->subsys_mask) {
/* Subsystem state should already exist */
BUG_ON(ss == NULL);
BUG_ON(!cgrp->subsys[i]);
@@ -1069,7 +1072,6 @@ static int rebind_subsystems(struct cgroupfs_root *root,
BUG_ON(cgrp->subsys[i]);
}
}
- root->subsys_mask = root->actual_subsys_mask = final_subsys_mask;
return 0;
}
@@ -1343,7 +1345,7 @@ static int cgroup_remount(struct super_block *sb, int *flags, char *data)
if (ret)
goto out_unlock;
- if (opts.subsys_mask != root->actual_subsys_mask || opts.release_agent)
+ if (opts.subsys_mask != root->subsys_mask || opts.release_agent)
pr_warning("cgroup: option changes via remount are deprecated (pid=%d comm=%s)\n",
task_tgid_nr(current), current->comm);
@@ -1365,7 +1367,7 @@ static int cgroup_remount(struct super_block *sb, int *flags, char *data)
*/
cgroup_clear_directory(cgrp->dentry, false, removed_mask);
- ret = rebind_subsystems(root, opts.subsys_mask);
+ ret = rebind_subsystems(root, added_mask, removed_mask);
if (ret) {
/* rebind_subsystems failed, re-populate the removed files */
cgroup_populate_dir(cgrp, false, removed_mask);
@@ -1634,7 +1636,7 @@ static struct dentry *cgroup_mount(struct file_system_type *fs_type,
if (ret)
goto unlock_drop;
- ret = rebind_subsystems(root, root->subsys_mask);
+ ret = rebind_subsystems(root, root->subsys_mask, 0);
if (ret == -EBUSY) {
free_cgrp_cset_links(&tmp_links);
goto unlock_drop;
@@ -1727,7 +1729,7 @@ static void cgroup_kill_sb(struct super_block *sb) {
mutex_lock(&cgroup_root_mutex);
/* Rebind all subsystems back to the default hierarchy */
- ret = rebind_subsystems(root, 0);
+ ret = rebind_subsystems(root, 0, root->subsys_mask);
/* Shouldn't be able to fail ... */
BUG_ON(ret);
--
1.8.2.1
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