[PATCH cgroup/for-3.14-fixes] cgroup: protect modifications to cgroup_idr with cgroup_mutex
From: Tejun Heo <hidden>
Date: 2014-02-11 15:41:12
Also in:
lkml
Subsystem:
control group (cgroup), the rest · Maintainers:
Tejun Heo, Johannes Weiner, Michal Koutný, Linus Torvalds
Hello,
This is the slightly modified patch that I applied to
cgroup/for-3.14-fixes.
Thanks a lot!
-------- 8< --------
From 0ab02ca8f887908152d1a96db5130fc661d36a1e Mon Sep 17 00:00:00 2001
From: Li Zefan <redacted>
Date: Tue, 11 Feb 2014 16:05:46 +0800
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: <redacted> #3.12+
Reported-by: Michal Hocko <redacted>
Signed-off-by: Li Zefan <redacted>
Signed-off-by: Tejun Heo <redacted>
---
include/linux/cgroup.h | 2 ++
kernel/cgroup.c | 34 ++++++++++++++++++----------------
2 files changed, 20 insertions(+), 16 deletions(-)
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 5c09759..9450f02 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h@@ -166,6 +166,8 @@ struct cgroup { * * The ID of the root cgroup is always 0, and a new cgroup * will be assigned with a smallest available ID. + * + * Allocating/Removing ID must be protected by cgroup_mutex. */ int id;
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 3edf716..52719ce 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:
--
1.8.5.3