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authorMichal Koutný <mkoutny@suse.com>2020-01-09 16:05:59 +0100
committerTejun Heo <tj@kernel.org>2020-01-15 08:04:29 -0800
commit3bc0bb36fa30e95ca829e9cf480e1ef7f7638333 (patch)
treecad37dd3b577ac44ac22a5da458812c43ec2106d /kernel/cgroup/cgroup.c
parent75ea91cd3eab8214eb8cd7f61ac23f41884d29ec (diff)
cgroup: Prevent double killing of css when enabling threaded cgroup
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>
Diffstat (limited to 'kernel/cgroup/cgroup.c')
-rw-r--r--kernel/cgroup/cgroup.c11
1 files changed, 6 insertions, 5 deletions
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 735af8f15f95..1e12e6928bca 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -3055,8 +3055,6 @@ static int cgroup_apply_control_enable(struct cgroup *cgrp)
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;
@@ -3066,6 +3064,8 @@ static int cgroup_apply_control_enable(struct cgroup *cgrp)
return PTR_ERR(css);
}
+ WARN_ON_ONCE(percpu_ref_is_dying(&css->refcnt));
+
if (css_visible(css)) {
ret = css_populate_dir(css);
if (ret)
@@ -3101,11 +3101,11 @@ static void cgroup_apply_control_disable(struct cgroup *cgrp)
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);
@@ -3392,7 +3392,8 @@ static ssize_t cgroup_type_write(struct kernfs_open_file *of, char *buf,
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;