From: Michal Koutný mkoutny@suse.com
commit 3bc0bb36fa30e95ca829e9cf480e1ef7f7638333 upstream.
The test_cgcore_no_internal_process_constraint_on_threads selftest when running with subsystem controlling noise triggers two warnings:
[ 597.443115] WARNING: CPU: 1 PID: 28167 at kernel/cgroup/cgroup.c:3131 cgroup_apply_control_enable+0xe0/0x3f0 [ 597.443413] WARNING: CPU: 1 PID: 28167 at kernel/cgroup/cgroup.c:3177 cgroup_apply_control_disable+0xa6/0x160
Both stem from a call to cgroup_type_write. The first warning was also triggered by syzkaller.
When we're switching cgroup to threaded mode shortly after a subsystem was disabled on it, we can see the respective subsystem css dying there.
The warning in cgroup_apply_control_enable is harmless in this case since we're not adding new subsys anyway. The warning in cgroup_apply_control_disable indicates an attempt to kill css of recently disabled subsystem repeatedly.
The commit prevents these situations by making cgroup_type_write wait for all dying csses to go away before re-applying subtree controls. When at it, the locations of WARN_ON_ONCE calls are moved so that warning is triggered only when we are about to misuse the dying css.
Reported-by: syzbot+5493b2a54d31d6aea629@syzkaller.appspotmail.com Reported-by: Christian Brauner christian.brauner@ubuntu.com Signed-off-by: Michal Koutný mkoutny@suse.com Signed-off-by: Tejun Heo tj@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- kernel/cgroup/cgroup.c | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-)
--- a/kernel/cgroup/cgroup.c +++ b/kernel/cgroup/cgroup.c @@ -2940,8 +2940,6 @@ static int cgroup_apply_control_enable(s for_each_subsys(ss, ssid) { struct cgroup_subsys_state *css = cgroup_css(dsct, ss);
- WARN_ON_ONCE(css && percpu_ref_is_dying(&css->refcnt)); - if (!(cgroup_ss_mask(dsct) & (1 << ss->id))) continue;
@@ -2951,6 +2949,8 @@ static int cgroup_apply_control_enable(s return PTR_ERR(css); }
+ WARN_ON_ONCE(percpu_ref_is_dying(&css->refcnt)); + if (css_visible(css)) { ret = css_populate_dir(css); if (ret) @@ -2986,11 +2986,11 @@ static void cgroup_apply_control_disable for_each_subsys(ss, ssid) { struct cgroup_subsys_state *css = cgroup_css(dsct, ss);
- WARN_ON_ONCE(css && percpu_ref_is_dying(&css->refcnt)); - if (!css) continue;
+ WARN_ON_ONCE(percpu_ref_is_dying(&css->refcnt)); + if (css->parent && !(cgroup_ss_mask(dsct) & (1 << ss->id))) { kill_css(css); @@ -3277,7 +3277,8 @@ static ssize_t cgroup_type_write(struct if (strcmp(strstrip(buf), "threaded")) return -EINVAL;
- cgrp = cgroup_kn_lock_live(of->kn, false); + /* drain dying csses before we re-apply (threaded) subtree control */ + cgrp = cgroup_kn_lock_live(of->kn, true); if (!cgrp) return -ENOENT;