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authorZefan Li <lizefan@huawei.com>2017-04-19 05:15:59 +0300
committerTejun Heo <tj@kernel.org>2017-04-29 01:04:54 +0300
commit9732adc5d6520238223df16630f1f8cad2269317 (patch)
treeb10b3242df285c38a45e4b8039b2e860a9e20def /kernel/cgroup
parenta590b90d472f2c176c140576ee3ab44df7f67839 (diff)
downloadlinux-9732adc5d6520238223df16630f1f8cad2269317.tar.xz
cgroup: avoid attaching a cgroup root to two different superblocks, take 2
Commit bfb0b80db5f9 ("cgroup: avoid attaching a cgroup root to two different superblocks") is broken. Now we try to fix the race by delaying the initialization of cgroup root refcnt until a superblock has been allocated. Reported-by: Dmitry Vyukov <dvyukov@google.com> Reported-by: Andrei Vagin <avagin@virtuozzo.com> Tested-by: Andrei Vagin <avagin@virtuozzo.com> Signed-off-by: Zefan Li <lizefan@huawei.com> Signed-off-by: Tejun Heo <tj@kernel.org>
Diffstat (limited to 'kernel/cgroup')
-rw-r--r--kernel/cgroup/cgroup-internal.h2
-rw-r--r--kernel/cgroup/cgroup-v1.c16
-rw-r--r--kernel/cgroup/cgroup.c8
3 files changed, 20 insertions, 6 deletions
diff --git a/kernel/cgroup/cgroup-internal.h b/kernel/cgroup/cgroup-internal.h
index 4567f12b02e9..00f4d6bf048f 100644
--- a/kernel/cgroup/cgroup-internal.h
+++ b/kernel/cgroup/cgroup-internal.h
@@ -164,7 +164,7 @@ int cgroup_path_ns_locked(struct cgroup *cgrp, char *buf, size_t buflen,
void cgroup_free_root(struct cgroup_root *root);
void init_cgroup_root(struct cgroup_root *root, struct cgroup_sb_opts *opts);
-int cgroup_setup_root(struct cgroup_root *root, u16 ss_mask);
+int cgroup_setup_root(struct cgroup_root *root, u16 ss_mask, int ref_flags);
int rebind_subsystems(struct cgroup_root *dst_root, u16 ss_mask);
struct dentry *cgroup_do_mount(struct file_system_type *fs_type, int flags,
struct cgroup_root *root, unsigned long magic,
diff --git a/kernel/cgroup/cgroup-v1.c b/kernel/cgroup/cgroup-v1.c
index c4a68c438fde..a478995e7ed3 100644
--- a/kernel/cgroup/cgroup-v1.c
+++ b/kernel/cgroup/cgroup-v1.c
@@ -1072,6 +1072,7 @@ struct dentry *cgroup1_mount(struct file_system_type *fs_type, int flags,
struct cgroup_subsys *ss;
struct dentry *dentry;
int i, ret;
+ bool new_root = false;
cgroup_lock_and_drain_offline(&cgrp_dfl_root.cgrp);
@@ -1181,10 +1182,11 @@ struct dentry *cgroup1_mount(struct file_system_type *fs_type, int flags,
ret = -ENOMEM;
goto out_unlock;
}
+ new_root = true;
init_cgroup_root(root, &opts);
- ret = cgroup_setup_root(root, opts.subsys_mask);
+ ret = cgroup_setup_root(root, opts.subsys_mask, PERCPU_REF_INIT_DEAD);
if (ret)
cgroup_free_root(root);
@@ -1201,6 +1203,18 @@ out_free:
CGROUP_SUPER_MAGIC, ns);
/*
+ * There's a race window after we release cgroup_mutex and before
+ * allocating a superblock. Make sure a concurrent process won't
+ * be able to re-use the root during this window by delaying the
+ * initialization of root refcnt.
+ */
+ if (new_root) {
+ mutex_lock(&cgroup_mutex);
+ percpu_ref_reinit(&root->cgrp.self.refcnt);
+ mutex_unlock(&cgroup_mutex);
+ }
+
+ /*
* If @pinned_sb, we're reusing an existing root and holding an
* extra ref on its sb. Mount is complete. Put the extra ref.
*/
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 10951d5e35d2..38d9386f46e7 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -1645,7 +1645,7 @@ void init_cgroup_root(struct cgroup_root *root, struct cgroup_sb_opts *opts)
set_bit(CGRP_CPUSET_CLONE_CHILDREN, &root->cgrp.flags);
}
-int cgroup_setup_root(struct cgroup_root *root, u16 ss_mask)
+int cgroup_setup_root(struct cgroup_root *root, u16 ss_mask, int ref_flags)
{
LIST_HEAD(tmp_links);
struct cgroup *root_cgrp = &root->cgrp;
@@ -1661,8 +1661,8 @@ int cgroup_setup_root(struct cgroup_root *root, u16 ss_mask)
root_cgrp->id = ret;
root_cgrp->ancestor_ids[0] = ret;
- ret = percpu_ref_init(&root_cgrp->self.refcnt, css_release, 0,
- GFP_KERNEL);
+ ret = percpu_ref_init(&root_cgrp->self.refcnt, css_release,
+ ref_flags, GFP_KERNEL);
if (ret)
goto out;
@@ -4517,7 +4517,7 @@ int __init cgroup_init(void)
hash_add(css_set_table, &init_css_set.hlist,
css_set_hash(init_css_set.subsys));
- BUG_ON(cgroup_setup_root(&cgrp_dfl_root, 0));
+ BUG_ON(cgroup_setup_root(&cgrp_dfl_root, 0, 0));
mutex_unlock(&cgroup_mutex);