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cgroup: remove cgroup->actual_subsys_mask 

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 @root>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 @root->actual_subsys_mask.

This patch shouldn't introduce any behavior changes.

v2: Comment and description updated as suggested by Li.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
This commit is contained in:
Tejun Heo 2013-06-24 15:21:47 -07:00
parent 9871bf9550
commit a8a648c4ac
2 changed files with 13 additions and 17 deletions
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8
include/linux/cgroup.h
View File

@ -286,18 +286,12 @@ enum {
struct cgroupfs_root {
struct super_block *sb;
/*
* The bitmask of subsystems intended to be attached to this
* hierarchy
*/
/* The bitmask of subsystems attached to this hierarchy */
unsigned long subsys_mask;
/* 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;

22
kernel/cgroup.c
View File

@ -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);