cgroup/pids: Avoid spurious event notification

Currently when a process in a group forks and fails due to it's
parent's max restriction, all the cgroups from 'pids_forking' to root
will generate event notifications but only the cgroups from
'pids_over_limit' to root will increase the counter of PIDCG_MAX.

Consider this scenario: there are 4 groups A, B, C,and D, the
relationships are as follows, and user is watching on C.pids.events.

root->A->B->C->D

When a process in D forks and fails due to B.max restriction, the
user will get a spurious event notification because when he wakes up
and reads C.pids.events, he will find that the content has not changed.

To address this issue, only the cgroups from 'pids_over_limit' to root
will have their PIDCG_MAX counters increased and event notifications
generated.

Fixes: 385a635cacfe ("cgroup/pids: Make event counters hierarchical")
Signed-off-by: Xiu Jianfeng <xiujianfeng@huawei.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

diff --git a/kernel/cgroup/pids.c b/kernel/cgroup/pids.c
index f5cb0ec45b9ddee9a7a3ce3bd85ab4161a2abbc5..34aa63d7c9c659ba1634148f3289a849901e88da 100644 (file)
--- a/kernel/cgroup/pids.c
+++ b/kernel/cgroup/pids.c
@@ -244,7 +244,6 @@ static void pids_event(struct pids_cgroup *pids_forking,
                       struct pids_cgroup *pids_over_limit)
 {
        struct pids_cgroup *p = pids_forking;
-       bool limit = false;
 
        /* Only log the first time limit is hit. */
        if (atomic64_inc_return(&p->events_local[PIDCG_FORKFAIL]) == 1) {
@@ -252,20 +251,17 @@ static void pids_event(struct pids_cgroup *pids_forking,
                pr_cont_cgroup_path(p->css.cgroup);
                pr_cont("\n");
        }
-       cgroup_file_notify(&p->events_local_file);
        if (!cgroup_subsys_on_dfl(pids_cgrp_subsys) ||
-           cgrp_dfl_root.flags & CGRP_ROOT_PIDS_LOCAL_EVENTS)
+           cgrp_dfl_root.flags & CGRP_ROOT_PIDS_LOCAL_EVENTS) {
+               cgroup_file_notify(&p->events_local_file);
                return;
+       }
 
-       for (; parent_pids(p); p = parent_pids(p)) {
-               if (p == pids_over_limit) {
-                       limit = true;
-                       atomic64_inc(&p->events_local[PIDCG_MAX]);
-                       cgroup_file_notify(&p->events_local_file);
-               }
-               if (limit)
-                       atomic64_inc(&p->events[PIDCG_MAX]);
+       atomic64_inc(&pids_over_limit->events_local[PIDCG_MAX]);
+       cgroup_file_notify(&pids_over_limit->events_local_file);
 
+       for (p = pids_over_limit; parent_pids(p); p = parent_pids(p)) {
+               atomic64_inc(&p->events[PIDCG_MAX]);
                cgroup_file_notify(&p->events_file);
        }
 }