Commit a8a648c4 authored by Tejun Heo's avatar Tejun Heo
Browse files

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: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarLi Zefan <lizefan@huawei.com>
parent 9871bf95

include/linux/cgroup.h

+1 −7
Original line number Diff line number Diff line
@@ -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;

kernel/cgroup.c

+12 −10
Original line number Diff line number Diff line
@@ -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);

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