linux-kernel - [RFC PATCH v3 3/9] cgroup/pids: Make event counters hierarchical

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Message-ID: <20240405170548.15234-4-mkoutny@suse.com>
Date: Fri,  5 Apr 2024 19:05:42 +0200
From: Michal Koutný <mkoutny@...e.com>
To: cgroups@...r.kernel.org,
	linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-kselftest@...r.kernel.org
Cc: Tejun Heo <tj@...nel.org>,
	Zefan Li <lizefan.x@...edance.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Jonathan Corbet <corbet@....net>,
	Shuah Khan <shuah@...nel.org>
Subject: [RFC PATCH v3 3/9] cgroup/pids: Make event counters hierarchical

The pids.events file should honor the hierarchy, so make the events
propagate from their origin up to the root on the unified hierarchy. The
v1 behavior remains non-hierarchical.

Signed-off-by: Michal Koutný <mkoutny@...e.com>
---
 Documentation/admin-guide/cgroup-v2.rst |  4 ++-
 kernel/cgroup/pids.c                    | 46 ++++++++++++++++---------
 2 files changed, 33 insertions(+), 17 deletions(-)

diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
index 4f04538d688c..5d4c505cae06 100644
--- a/Documentation/admin-guide/cgroup-v2.rst
+++ b/Documentation/admin-guide/cgroup-v2.rst
@@ -2189,7 +2189,9 @@ PID Interface Files
   pids.events
 	A read-only flat-keyed file which exists on non-root cgroups.  Unless
 	specified otherwise, a value change in this file generates a file modified
-	event. The following entries are defined.
+	event. Fields in this file are hierarchical and the file modified event
+	can be generated due to an event down the hierarchy. The following
+	entries are defined.
 
 	  max
 		The number of times the limit of the cgroup was hit.
diff --git a/kernel/cgroup/pids.c b/kernel/cgroup/pids.c
index 471562609eef..76c0a97e42da 100644
--- a/kernel/cgroup/pids.c
+++ b/kernel/cgroup/pids.c
@@ -238,6 +238,34 @@ static void pids_cancel_attach(struct cgroup_taskset *tset)
 	}
 }
 
+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[PIDCG_MAX_IMPOSED]) == 1) {
+		pr_info("cgroup: fork rejected by pids controller in ");
+		pr_cont_cgroup_path(p->css.cgroup);
+		pr_cont("\n");
+	}
+	/* Events are only notified in pids_forking on v1 */
+	if (!cgroup_subsys_on_dfl(pids_cgrp_subsys))
+		return;
+
+	for (; parent_pids(p); p = parent_pids(p)) {
+		atomic64_inc(&p->events[PIDCG_MAX_IMPOSED]);
+
+		if (p == pids_over_limit)
+			limit = true;
+		if (limit)
+			atomic64_inc(&p->events[PIDCG_MAX]);
+
+		cgroup_file_notify(&p->events_file);
+	}
+}
+
 /*
  * task_css_check(true) in pids_can_fork() and pids_cancel_fork() relies
  * on cgroup_threadgroup_change_begin() held by the copy_process().
@@ -254,23 +282,9 @@ static int pids_can_fork(struct task_struct *task, struct css_set *cset)
 		css = task_css_check(current, pids_cgrp_id, true);
 	pids = css_pids(css);
 	err = pids_try_charge(pids, 1, &pids_over_limit);
-	if (err) {
-		/* compatibility on v1 where events were notified in leaves. */
-		if (!cgroup_subsys_on_dfl(pids_cgrp_subsys))
-			pids_over_limit = pids;
-
-		/* Only log the first time limit is hit. */
-		if (atomic64_inc_return(&pids->events[PIDCG_MAX_IMPOSED]) == 1) {
-			pr_info("cgroup: fork rejected by pids controller in ");
-			pr_cont_cgroup_path(pids->css.cgroup);
-			pr_cont("\n");
-		}
-		atomic64_inc(&pids_over_limit->events[PIDCG_MAX]);
+	if (err)
+		pids_event(pids, pids_over_limit);
 
-		cgroup_file_notify(&pids->events_file);
-		if (pids_over_limit != pids)
-			cgroup_file_notify(&pids_over_limit->events_file);
-	}
 	return err;
 }
 
-- 
2.44.0