Commit 6fa4918d authored by Tejun Heo's avatar Tejun Heo
Browse files

cgroup: protect cgroup_root->cgroup_idr with a spinlock 



Currently, cgroup_root->cgroup_idr is protected by cgroup_mutex, which
ends up requiring cgroup_put() to be invoked under sleepable context.
This is okay for now but is an unusual requirement and we'll soon add
css->id which will have the same problem but won't be able to simply
grab cgroup_mutex as removal will have to happen from css_release()
which can't sleep.

Introduce cgroup_idr_lock and idr_alloc/replace/remove() wrappers
which protects the idr operations with the lock and use them for
cgroup_root->cgroup_idr.  cgroup_put() no longer needs to grab
cgroup_mutex and css_from_id() is updated to always require RCU read
lock instead of either RCU read lock or cgroup_mutex, which doesn't
affect the existing users.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarLi Zefan <lizefan@huawei.com>
parent 7d699ddb

kernel/cgroup.c

+43 −8
Original line number Diff line number Diff line
@@ -99,6 +99,12 @@ static DEFINE_MUTEX(cgroup_mutex); 
static DECLARE_RWSEM(css_set_rwsem);

#endif



/*

 * Protects cgroup_idr so that IDs can be released without grabbing

 * cgroup_mutex.

 */

static DEFINE_SPINLOCK(cgroup_idr_lock);



/*

 * Protects cgroup_subsys->release_agent_path.  Modifying it also requires

 * cgroup_mutex.  Reading requires either cgroup_mutex or this spinlock.
@@ -190,6 +196,37 @@ static int cgroup_addrm_files(struct cgroup *cgrp, struct cftype cfts[], 
			      bool is_add);

static void cgroup_pidlist_destroy_all(struct cgroup *cgrp);



/* IDR wrappers which synchronize using cgroup_idr_lock */

static int cgroup_idr_alloc(struct idr *idr, void *ptr, int start, int end,

			    gfp_t gfp_mask)

{

	int ret;



	idr_preload(gfp_mask);

	spin_lock(&cgroup_idr_lock);

	ret = idr_alloc(idr, ptr, start, end, gfp_mask);

	spin_unlock(&cgroup_idr_lock);

	idr_preload_end();

	return ret;

}



static void *cgroup_idr_replace(struct idr *idr, void *ptr, int id)

{

	void *ret;



	spin_lock(&cgroup_idr_lock);

	ret = idr_replace(idr, ptr, id);

	spin_unlock(&cgroup_idr_lock);

	return ret;

}



static void cgroup_idr_remove(struct idr *idr, int id)

{

	spin_lock(&cgroup_idr_lock);

	idr_remove(idr, id);

	spin_unlock(&cgroup_idr_lock);

}



/**

 * cgroup_css - obtain a cgroup's css for the specified subsystem

 * @cgrp: the cgroup of interest
@@ -1058,9 +1095,7 @@ static void cgroup_put(struct cgroup *cgrp) 
	 * per-subsystem and moved to css->id so that lookups are

	 * successful until the target css is released.

	 */

	mutex_lock(&cgroup_mutex);

	idr_remove(&cgrp->root->cgroup_idr, cgrp->id);

	mutex_unlock(&cgroup_mutex);

	cgroup_idr_remove(&cgrp->root->cgroup_idr, cgrp->id);

	cgrp->id = -1;



	call_rcu(&cgrp->rcu_head, cgroup_free_rcu);
@@ -1531,7 +1566,7 @@ static int cgroup_setup_root(struct cgroup_root *root, unsigned int ss_mask) 
	lockdep_assert_held(&cgroup_tree_mutex);

	lockdep_assert_held(&cgroup_mutex);



	ret = idr_alloc(&root->cgroup_idr, root_cgrp, 1, 2, GFP_KERNEL);

	ret = cgroup_idr_alloc(&root->cgroup_idr, root_cgrp, 1, 2, GFP_NOWAIT);

	if (ret < 0)

		goto out;

	root_cgrp->id = ret;
@@ -4225,7 +4260,7 @@ static long cgroup_create(struct cgroup *parent, const char *name, 
	 * Temporarily set the pointer to NULL, so idr_find() won't return

	 * a half-baked cgroup.

	 */

	cgrp->id = idr_alloc(&root->cgroup_idr, NULL, 2, 0, GFP_KERNEL);

	cgrp->id = cgroup_idr_alloc(&root->cgroup_idr, NULL, 2, 0, GFP_NOWAIT);

	if (cgrp->id < 0) {

		err = -ENOMEM;

		goto err_unlock;
@@ -4268,7 +4303,7 @@ static long cgroup_create(struct cgroup *parent, const char *name, 
	 * @cgrp is now fully operational.  If something fails after this

	 * point, it'll be released via the normal destruction path.

	 */

	idr_replace(&root->cgroup_idr, cgrp, cgrp->id);

	cgroup_idr_replace(&root->cgroup_idr, cgrp, cgrp->id);



	err = cgroup_kn_set_ugid(kn);

	if (err)
@@ -4302,7 +4337,7 @@ static long cgroup_create(struct cgroup *parent, const char *name, 
	return 0;



err_free_id:

	idr_remove(&root->cgroup_idr, cgrp->id);

	cgroup_idr_remove(&root->cgroup_idr, cgrp->id);

err_unlock:

	mutex_unlock(&cgroup_mutex);

err_unlock_tree:
@@ -5162,7 +5197,7 @@ struct cgroup_subsys_state *css_from_id(int id, struct cgroup_subsys *ss) 
{

	struct cgroup *cgrp;



	cgroup_assert_mutexes_or_rcu_locked();

	WARN_ON_ONCE(!rcu_read_lock_held());



	cgrp = idr_find(&ss->root->cgroup_idr, id);

	if (cgrp)

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