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Tue, 04 Mar 2025 07:38:52 -0800 (PST) From: =?utf-8?q?Michal_Koutn=C3=BD?= To: cgroups@vger.kernel.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Tejun Heo , Josef Bacik , Jens Axboe , Johannes Weiner , =?utf-8?q?Michal_Koutn=C3=BD?= , Waiman Long Subject: [PATCH 4/9] cgroup: Print warning when /proc/cgroups is read on v2-only system Date: Tue, 4 Mar 2025 16:37:56 +0100 Message-ID: <20250304153801.597907-5-mkoutny@suse.com> X-Mailer: git-send-email 2.48.1 In-Reply-To: <20250304153801.597907-1-mkoutny@suse.com> References: <20250304153801.597907-1-mkoutny@suse.com> Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 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 neven mount v2 but read /proc/cgroups upon boot when controllers default to v2). Signed-off-by: Michal Koutný Acked-by: Waiman Long --- 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 c964dd7ff967a..95ab39e1ec8f0 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 e28d5f0d20ed0..5c59b01024019 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_warn_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 afc665b7b1fe5..3a5af0fc544a6 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;