linux-kernel - [PATCH cgroup/for-5.5] cgroup: fix incorrect WARN_ON_ONCE() in cgroup_setup

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Date:   Thu, 14 Nov 2019 14:54:08 -0800
From:   Tejun Heo <tj@...nel.org>
To:     Naresh Kamboju <naresh.kamboju@...aro.org>
Cc:     cgroups@...r.kernel.org,
        Linux-Next Mailing List <linux-next@...r.kernel.org>,
        namhyung@...nel.org, open list <linux-kernel@...r.kernel.org>,
        lkft-triage@...ts.linaro.org, lizefan@...wei.com,
        hannes@...xchg.org, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>, kafai@...com,
        Song Liu <songliubraving@...com>
Subject: [PATCH cgroup/for-5.5] cgroup: fix incorrect WARN_ON_ONCE() in
 cgroup_setup_root()

Never mind.  I just failed to see the warning on x86_32.  The warning
is spurious and fixed with the following commit.  Applied to
cgroup/for-5.5.

Thanks.

------ 8< ------
>From d7495343228f30d8206e92dccfd1c41adcfa142d Mon Sep 17 00:00:00 2001
From: Tejun Heo <tj@...nel.org>
Date: Thu, 14 Nov 2019 14:46:51 -0800

743210386c03 ("cgroup: use cgrp->kn->id as the cgroup ID") added WARN
which triggers if cgroup_id(root_cgrp) is not 1.  This is fine on
64bit ino archs but on 32bit archs cgroup ID is ((gen << 32) | ino)
and gen starts at 1, so the root id is 0x1_0000_0001 instead of 1
always triggering the WARN.

What we wanna make sure is that the ino part is 1.  Fix it.

Reported-by: Naresh Kamboju <naresh.kamboju@...aro.org>
Fixes: 743210386c03 ("cgroup: use cgrp->kn->id as the cgroup ID")
Signed-off-by: Tejun Heo <tj@...nel.org>
---
 kernel/cgroup/cgroup.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index c12dcf7dc432..53098c1d45e2 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -1966,7 +1966,7 @@ int cgroup_setup_root(struct cgroup_root *root, u16 ss_mask)
 		goto exit_root_id;
 	}
 	root_cgrp->kn = root->kf_root->kn;
-	WARN_ON_ONCE(cgroup_id(root_cgrp) != 1);
+	WARN_ON_ONCE(cgroup_ino(root_cgrp) != 1);
 	root_cgrp->ancestor_ids[0] = cgroup_id(root_cgrp);
 
 	ret = css_populate_dir(&root_cgrp->self);
-- 
2.17.1