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authorLi Zefan <lizefan@huawei.com>2014-02-11 16:05:46 +0800
committerTejun Heo <tj@kernel.org>2014-02-11 10:38:30 -0500
commit0ab02ca8f887908152d1a96db5130fc661d36a1e (patch)
tree81f7be1f4da646a88ab09bd7c01927a4f2a180bf /kernel
parent48573a893303986e3b0b2974d6fb11f3d1bb7064 (diff)
downloadlinux-0ab02ca8f887908152d1a96db5130fc661d36a1e.tar.gz
cgroup: protect modifications to cgroup_idr with cgroup_mutex
Setup cgroupfs like this: # mount -t cgroup -o cpuacct xxx /cgroup # mkdir /cgroup/sub1 # mkdir /cgroup/sub2 Then run these two commands: # for ((; ;)) { mkdir /cgroup/sub1/tmp && rmdir /mnt/sub1/tmp; } & # for ((; ;)) { mkdir /cgroup/sub2/tmp && rmdir /mnt/sub2/tmp; } & After seconds you may see this warning: ------------[ cut here ]------------ WARNING: CPU: 1 PID: 25243 at lib/idr.c:527 sub_remove+0x87/0x1b0() idr_remove called for id=6 which is not allocated. ... Call Trace: [<ffffffff8156063c>] dump_stack+0x7a/0x96 [<ffffffff810591ac>] warn_slowpath_common+0x8c/0xc0 [<ffffffff81059296>] warn_slowpath_fmt+0x46/0x50 [<ffffffff81300aa7>] sub_remove+0x87/0x1b0 [<ffffffff810f3f02>] ? css_killed_work_fn+0x32/0x1b0 [<ffffffff81300bf5>] idr_remove+0x25/0xd0 [<ffffffff810f2bab>] cgroup_destroy_css_killed+0x5b/0xc0 [<ffffffff810f4000>] css_killed_work_fn+0x130/0x1b0 [<ffffffff8107cdbc>] process_one_work+0x26c/0x550 [<ffffffff8107eefe>] worker_thread+0x12e/0x3b0 [<ffffffff81085f96>] kthread+0xe6/0xf0 [<ffffffff81570bac>] ret_from_fork+0x7c/0xb0 ---[ end trace 2d1577ec10cf80d0 ]--- It's because allocating/removing cgroup ID is not properly synchronized. The bug was introduced when we converted cgroup_ida to cgroup_idr. While synchronization is already done inside ida_simple_{get,remove}(), users are responsible for concurrent calls to idr_{alloc,remove}(). tj: Refreshed on top of b58c89986a77 ("cgroup: fix error return from cgroup_create()"). Fixes: 4e96ee8e981b ("cgroup: convert cgroup_ida to cgroup_idr") Cc: <stable@vger.kernel.org> #3.12+ Reported-by: Michal Hocko <mhocko@suse.cz> Signed-off-by: Li Zefan <lizefan@huawei.com> Signed-off-by: Tejun Heo <tj@kernel.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/cgroup.c34
1 files changed, 18 insertions, 16 deletions
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 3edf7163b84..52719ce55dd 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -886,7 +886,9 @@ static void cgroup_diput(struct dentry *dentry, struct inode *inode)
* 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);
cgrp->id = -1;
call_rcu(&cgrp->rcu_head, cgroup_free_rcu);
@@ -4168,16 +4170,6 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
rcu_assign_pointer(cgrp->name, 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, 1, 0, GFP_KERNEL);
- if (cgrp->id < 0) {
- err = -ENOMEM;
- goto err_free_name;
- }
-
- /*
* Only live parents can have children. Note that the liveliness
* check isn't strictly necessary because cgroup_mkdir() and
* cgroup_rmdir() are fully synchronized by i_mutex; however, do it
@@ -4186,7 +4178,17 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
*/
if (!cgroup_lock_live_group(parent)) {
err = -ENODEV;
- goto err_free_id;
+ goto err_free_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, 1, 0, GFP_KERNEL);
+ if (cgrp->id < 0) {
+ err = -ENOMEM;
+ goto err_unlock;
}
/* Grab a reference on the superblock so the hierarchy doesn't
@@ -4218,7 +4220,7 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
*/
err = cgroup_create_file(dentry, S_IFDIR | mode, sb);
if (err < 0)
- goto err_unlock;
+ goto err_free_id;
lockdep_assert_held(&dentry->d_inode->i_mutex);
cgrp->serial_nr = cgroup_serial_nr_next++;
@@ -4254,12 +4256,12 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
return 0;
-err_unlock:
- mutex_unlock(&cgroup_mutex);
- /* Release the reference count that we took on the superblock */
- deactivate_super(sb);
err_free_id:
idr_remove(&root->cgroup_idr, cgrp->id);
+ /* Release the reference count that we took on the superblock */
+ deactivate_super(sb);
+err_unlock:
+ mutex_unlock(&cgroup_mutex);
err_free_name:
kfree(rcu_dereference_raw(cgrp->name));
err_free_cgrp: