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Commit 146aa1bd authored by Lai Jiangshan's avatar Lai Jiangshan Committed by Linus Torvalds
Browse files

cgroups: fix probable race with put_css_set[_taskexit] and find_css_set 



put_css_set_taskexit may be called when find_css_set is called on other
cpu.  And the race will occur:

put_css_set_taskexit side                    find_css_set side

                                        |
atomic_dec_and_test(&kref->refcount)    |
    /* kref->refcount = 0 */            |
....................................................................
                                        |  read_lock(&css_set_lock)
                                        |  find_existing_css_set
                                        |  get_css_set
                                        |  read_unlock(&css_set_lock);
....................................................................
__release_css_set                       |
....................................................................
                                        | /* use a released css_set */
                                        |

[put_css_set is the same. But in the current code, all put_css_set are
put into cgroup mutex critical region as the same as find_css_set.]

[akpm@linux-foundation.org: repair comments]
[menage@google.com: eliminate race in css_set refcounting]
Signed-off-by: default avatarLai Jiangshan <laijs@cn.fujitsu.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: default avatarPaul Menage <menage@google.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 248736c2

include/linux/cgroup.h

+1 −2
Original line number Diff line number Diff line
@@ -9,7 +9,6 @@ 
 */



#include <linux/sched.h>

#include <linux/kref.h>

#include <linux/cpumask.h>

#include <linux/nodemask.h>

#include <linux/rcupdate.h>
@@ -149,7 +148,7 @@ struct cgroup { 
struct css_set {



	/* Reference count */

	struct kref ref;

	atomic_t refcount;



	/*

	 * List running through all cgroup groups in the same hash

kernel/cgroup.c

+20 −23
Original line number Diff line number Diff line
@@ -241,7 +241,6 @@ static void unlink_css_set(struct css_set *cg) 
	struct cg_cgroup_link *link;

	struct cg_cgroup_link *saved_link;



	write_lock(&css_set_lock);

	hlist_del(&cg->hlist);

	css_set_count--;
@@ -251,16 +250,25 @@ static void unlink_css_set(struct css_set *cg) 
		list_del(&link->cgrp_link_list);

		kfree(link);

	}



	write_unlock(&css_set_lock);

}



static void __release_css_set(struct kref *k, int taskexit)

static void __put_css_set(struct css_set *cg, int taskexit)

{

	int i;

	struct css_set *cg = container_of(k, struct css_set, ref);



	/*

	 * Ensure that the refcount doesn't hit zero while any readers

	 * can see it. Similar to atomic_dec_and_lock(), but for an

	 * rwlock

	 */

	if (atomic_add_unless(&cg->refcount, -1, 1))

		return;

	write_lock(&css_set_lock);

	if (!atomic_dec_and_test(&cg->refcount)) {

		write_unlock(&css_set_lock);

		return;

	}

	unlink_css_set(cg);

	write_unlock(&css_set_lock);



	rcu_read_lock();

	for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
@@ -276,32 +284,22 @@ static void __release_css_set(struct kref *k, int taskexit) 
	kfree(cg);

}



static void release_css_set(struct kref *k)

{

	__release_css_set(k, 0);

}



static void release_css_set_taskexit(struct kref *k)

{

	__release_css_set(k, 1);

}



/*

 * refcounted get/put for css_set objects

 */

static inline void get_css_set(struct css_set *cg)

{

	kref_get(&cg->ref);

	atomic_inc(&cg->refcount);

}



static inline void put_css_set(struct css_set *cg)

{

	kref_put(&cg->ref, release_css_set);

	__put_css_set(cg, 0);

}



static inline void put_css_set_taskexit(struct css_set *cg)

{

	kref_put(&cg->ref, release_css_set_taskexit);

	__put_css_set(cg, 1);

}



/*
@@ -427,7 +425,7 @@ static struct css_set *find_css_set( 
		return NULL;

	}



	kref_init(&res->ref);

	atomic_set(&res->refcount, 1);

	INIT_LIST_HEAD(&res->cg_links);

	INIT_LIST_HEAD(&res->tasks);

	INIT_HLIST_NODE(&res->hlist);
@@ -1728,7 +1726,7 @@ int cgroup_task_count(const struct cgroup *cgrp) 


	read_lock(&css_set_lock);

	list_for_each_entry(link, &cgrp->css_sets, cgrp_link_list) {

		count += atomic_read(&link->cg->ref.refcount);

		count += atomic_read(&link->cg->refcount);

	}

	read_unlock(&css_set_lock);

	return count;
@@ -2495,8 +2493,7 @@ static void __init cgroup_init_subsys(struct cgroup_subsys *ss) 
int __init cgroup_init_early(void)

{

	int i;

	kref_init(&init_css_set.ref);

	kref_get(&init_css_set.ref);

	atomic_set(&init_css_set.refcount, 1);

	INIT_LIST_HEAD(&init_css_set.cg_links);

	INIT_LIST_HEAD(&init_css_set.tasks);

	INIT_HLIST_NODE(&init_css_set.hlist);

kernel/cgroup_debug.c

+2 −2
Original line number Diff line number Diff line
@@ -57,7 +57,7 @@ static u64 current_css_set_refcount_read(struct cgroup *cont, 
	u64 count;



	rcu_read_lock();

	count = atomic_read(&current->cgroups->ref.refcount);

	count = atomic_read(&current->cgroups->refcount);

	rcu_read_unlock();

	return count;

}
@@ -90,7 +90,7 @@ static struct cftype files[] = { 
	{

		.name = "releasable",

		.read_u64 = releasable_read,

	}

	},

};



static int debug_populate(struct cgroup_subsys *ss, struct cgroup *cont)