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Commit 73e80ed8 authored by Tejun Heo's avatar Tejun Heo
Browse files

cgroup: add __rcu modifier to cgroup->subsys[] 



For the planned unified hierarchy, each css (cgroup_subsys_state) will
be RCU protected so that it can be created and destroyed individually
while allowing RCU accesses.  Previous changes ensured that all
cgroup->subsys[] accesses use the cgroup_css() accessor.  This patch
adds __rcu modifier to cgroup->subsys[], add matching RCU dereference
in cgroup_css() and convert all assignments to either
rcu_assign_pointer() or RCU_INIT_POINTER().

This change prepares for the actual RCUfication of css's and doesn't
introduce any visible behavior change.  The conversion is verified
with sparse and all accesses are properly RCU annotated.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarLi Zefan <lizefan@huawei.com>
parent 105347ba

include/linux/cgroup.h

+1 −1
Original line number Original line Diff line number Diff line
@@ -204,7 +204,7 @@ struct cgroup { 
	struct cgroup_name __rcu *name;

	struct cgroup_name __rcu *name;





	/* Private pointers for each registered subsystem */

	/* Private pointers for each registered subsystem */

	struct cgroup_subsys_state *subsys[CGROUP_SUBSYS_COUNT];

	struct cgroup_subsys_state __rcu *subsys[CGROUP_SUBSYS_COUNT];





	struct cgroupfs_root *root;

	struct cgroupfs_root *root;

kernel/cgroup.c

+14 −5
Original line number Original line Diff line number Diff line
@@ -229,11 +229,16 @@ static int cgroup_addrm_files(struct cgroup *cgrp, struct cftype cfts[], 
 * @subsys_id: the subsystem of interest

 * @subsys_id: the subsystem of interest

 *

 *

 * Return @cgrp's css (cgroup_subsys_state) associated with @subsys_id.

 * Return @cgrp's css (cgroup_subsys_state) associated with @subsys_id.

 * This function must be called either under cgroup_mutex or

 * rcu_read_lock() and the caller is responsible for pinning the returned

 * css if it wants to keep accessing it outside the said locks.  This

 * function may return %NULL if @cgrp doesn't have @subsys_id enabled.

 */

 */

static struct cgroup_subsys_state *cgroup_css(struct cgroup *cgrp,

static struct cgroup_subsys_state *cgroup_css(struct cgroup *cgrp,

					      int subsys_id)

					      int subsys_id)

{

{

	return cgrp->subsys[subsys_id];

	return rcu_dereference_check(cgrp->subsys[subsys_id],

				     lockdep_is_held(&cgroup_mutex));

}

}





/* convenient tests for these bits */

/* convenient tests for these bits */
@@ -1072,8 +1077,10 @@ static int rebind_subsystems(struct cgroupfs_root *root, 
			BUG_ON(!cgroup_css(cgroup_dummy_top, i));

			BUG_ON(!cgroup_css(cgroup_dummy_top, i));

			BUG_ON(cgroup_css(cgroup_dummy_top, i)->cgroup != cgroup_dummy_top);

			BUG_ON(cgroup_css(cgroup_dummy_top, i)->cgroup != cgroup_dummy_top);





			cgrp->subsys[i] = cgroup_dummy_top->subsys[i];

			rcu_assign_pointer(cgrp->subsys[i],

					   cgroup_css(cgroup_dummy_top, i));

			cgroup_css(cgrp, i)->cgroup = cgrp;

			cgroup_css(cgrp, i)->cgroup = cgrp;



			list_move(&ss->sibling, &root->subsys_list);

			list_move(&ss->sibling, &root->subsys_list);

			ss->root = root;

			ss->root = root;

			if (ss->bind)

			if (ss->bind)
@@ -1088,8 +1095,10 @@ static int rebind_subsystems(struct cgroupfs_root *root, 




			if (ss->bind)

			if (ss->bind)

				ss->bind(cgroup_css(cgroup_dummy_top, i));

				ss->bind(cgroup_css(cgroup_dummy_top, i));



			cgroup_css(cgroup_dummy_top, i)->cgroup = cgroup_dummy_top;

			cgroup_css(cgroup_dummy_top, i)->cgroup = cgroup_dummy_top;

			cgrp->subsys[i] = NULL;

			RCU_INIT_POINTER(cgrp->subsys[i], NULL);



			cgroup_subsys[i]->root = &cgroup_dummy_root;

			cgroup_subsys[i]->root = &cgroup_dummy_root;

			list_move(&ss->sibling, &cgroup_dummy_root.subsys_list);

			list_move(&ss->sibling, &cgroup_dummy_root.subsys_list);
@@ -4314,7 +4323,7 @@ static void init_cgroup_css(struct cgroup_subsys_state *css, 
		css->flags |= CSS_ROOT;

		css->flags |= CSS_ROOT;





	BUG_ON(cgroup_css(cgrp, ss->subsys_id));

	BUG_ON(cgroup_css(cgrp, ss->subsys_id));

	cgrp->subsys[ss->subsys_id] = css;

	rcu_assign_pointer(cgrp->subsys[ss->subsys_id], css);

}

}





/* invoke ->css_online() on a new CSS and mark it online if successful */

/* invoke ->css_online() on a new CSS and mark it online if successful */
@@ -4962,7 +4971,7 @@ void cgroup_unload_subsys(struct cgroup_subsys *ss) 
	 * also takes care of freeing the css_id.

	 * also takes care of freeing the css_id.

	 */

	 */

	ss->css_free(cgroup_css(cgroup_dummy_top, ss->subsys_id));

	ss->css_free(cgroup_css(cgroup_dummy_top, ss->subsys_id));

	cgroup_dummy_top->subsys[ss->subsys_id] = NULL;

	RCU_INIT_POINTER(cgroup_dummy_top->subsys[ss->subsys_id], NULL);





	mutex_unlock(&cgroup_mutex);

	mutex_unlock(&cgroup_mutex);

}

}