Bugzilla: 1045775
Upstream-status: queued for 3.14-rc3 and stable 3.12+
Path: news.gmane.org!not-for-mail
From: Michal Hocko <mhocko@suse.cz>
Newsgroups: gmane.linux.kernel,gmane.linux.kernel.cgroups
Subject: Re: [PATCH] cgroup: protect modifications to cgroup_idr with
cgroup_mutex
Date: Wed, 12 Feb 2014 10:12:38 +0100
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Approved: news@gmane.org
Message-ID: <20140212091238.GC28085@dhcp22.suse.cz>
References: <52F9D9DA.7040108@huawei.com>
<20140211102032.GA11946@dhcp22.suse.cz>
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Cc: Tejun Heo <tj@kernel.org>, LKML <linux-kernel@vger.kernel.org>,
Cgroups <cgroups@vger.kernel.org>
To: Li Zefan <lizefan@huawei.com>
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Li has pointed out that my previous backport was not correct because
err_unlock label releases a reference to supperblock which was not taken
before idr_alloc. I've also removed cgroup_mutex from free_css_id as per
Li.
Fixed in this version.
---
Date: Tue, 11 Feb 2014 16:05:46 +0800
From: Li Zefan <lizefan@huawei.com>
Subject: [PATCH - for 3.12] 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}().
[mhocko@suse.cz: ported to 3.12]
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: Michal Hocko <mhocko@suse.cz>
---
include/linux/cgroup.h | 2 ++
kernel/cgroup.c | 23 ++++++++++++-----------
2 files changed, 14 insertions(+), 11 deletions(-)
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -169,6 +169,8 @@ 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;
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -4410,14 +4410,6 @@ static long cgroup_create(struct cgroup
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)
- 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
@@ -4426,7 +4418,7 @@ static long cgroup_create(struct cgroup
*/
if (!cgroup_lock_live_group(parent)) {
err = -ENODEV;
- goto err_free_id;
+ goto err_free_name;
}
/* Grab a reference on the superblock so the hierarchy doesn't
@@ -4436,6 +4428,14 @@ static long cgroup_create(struct cgroup
* fs */
atomic_inc(&sb->s_active);
+ /*
+ * 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)
+ goto err_unlock;
+
init_cgroup_housekeeping(cgrp);
dentry->d_fsdata = cgrp;
@@ -4542,11 +4542,11 @@ err_free_all:
ss->css_free(css);
}
}
+ idr_remove(&root->cgroup_idr, cgrp->id);
+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);
err_free_name:
kfree(rcu_dereference_raw(cgrp->name));
err_free_cgrp:
--
Michal Hocko
SUSE Labs