From a0ab1453226d862cf30fdccc5a8e753f79c5bc99 Mon Sep 17 00:00:00 2001 From: =?utf8?q?Michal=20Koutn=C3=BD?= Date: Tue, 11 Mar 2025 13:36:21 +0100 Subject: [PATCH] cgroup: Print message when /proc/cgroups is read on v2-only system MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit As a followup to commits 6c2920926b10e ("cgroup: replace unified-hierarchy.txt with a proper cgroup v2 documentation") and ab03125268679 ("cgroup: Show # of subsystem CSSes in cgroup.stat"), add a runtime message to users who read status of controllers in /proc/cgroups on v2-only system. The detection is based on a) no controllers are attached to v1, b) default hierarchy is mounted (the latter is for setups that never mount v2 but read /proc/cgroups upon boot when controllers default to v2, so that this code may be backported to older kernels). Signed-off-by: Michal Koutný Acked-by: Waiman Long Signed-off-by: Tejun Heo --- kernel/cgroup/cgroup-internal.h | 1 + kernel/cgroup/cgroup-v1.c | 7 +++++++ kernel/cgroup/cgroup.c | 2 +- 3 files changed, 9 insertions(+), 1 deletion(-) diff --git a/kernel/cgroup/cgroup-internal.h b/kernel/cgroup/cgroup-internal.h index c964dd7ff967..95ab39e1ec8f 100644 --- a/kernel/cgroup/cgroup-internal.h +++ b/kernel/cgroup/cgroup-internal.h @@ -168,6 +168,7 @@ struct cgroup_mgctx { extern struct cgroup_subsys *cgroup_subsys[]; extern struct list_head cgroup_roots; +extern bool cgrp_dfl_visible; /* iterate across the hierarchies */ #define for_each_root(root) \ diff --git a/kernel/cgroup/cgroup-v1.c b/kernel/cgroup/cgroup-v1.c index e28d5f0d20ed..11ea8d24ac72 100644 --- a/kernel/cgroup/cgroup-v1.c +++ b/kernel/cgroup/cgroup-v1.c @@ -673,6 +673,7 @@ struct cftype cgroup1_base_files[] = { int proc_cgroupstats_show(struct seq_file *m, void *v) { struct cgroup_subsys *ss; + bool cgrp_v1_visible = false; int i; seq_puts(m, "#subsys_name\thierarchy\tnum_cgroups\tenabled\n"); @@ -684,12 +685,18 @@ int proc_cgroupstats_show(struct seq_file *m, void *v) for_each_subsys(ss, i) { if (cgroup1_subsys_absent(ss)) continue; + cgrp_v1_visible |= ss->root != &cgrp_dfl_root; + seq_printf(m, "%s\t%d\t%d\t%d\n", ss->legacy_name, ss->root->hierarchy_id, atomic_read(&ss->root->nr_cgrps), cgroup_ssid_enabled(i)); } + if (cgrp_dfl_visible && !cgrp_v1_visible) + pr_info_once("/proc/cgroups lists only v1 controllers, use cgroup.controllers of root cgroup for v2 info\n"); + + return 0; } diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c index 805764cf14e2..a810952d75c8 100644 --- a/kernel/cgroup/cgroup.c +++ b/kernel/cgroup/cgroup.c @@ -171,7 +171,7 @@ EXPORT_SYMBOL_GPL(cgrp_dfl_root); * The default hierarchy always exists but is hidden until mounted for the * first time. This is for backward compatibility. */ -static bool cgrp_dfl_visible; +bool cgrp_dfl_visible; /* some controllers are not supported in the default hierarchy */ static u16 cgrp_dfl_inhibit_ss_mask; -- 2.50.1