linux-kernel - [PATCH 5.4 027/120] cgroup: Add missing cpus_read_lock() to cgroup_attach_task

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Message-Id: <20220926100751.633857388@linuxfoundation.org>
Date:   Mon, 26 Sep 2022 12:11:00 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        syzbot <syzbot+29d3a3b4d86c8136ad9e@...kaller.appspotmail.com>,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        Tejun Heo <tj@...nel.org>
Subject: [PATCH 5.4 027/120] cgroup: Add missing cpus_read_lock() to cgroup_attach_task_all()

From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>

commit 43626dade36fa74d3329046f4ae2d7fdefe401c6 upstream.

syzbot is hitting percpu_rwsem_assert_held(&cpu_hotplug_lock) warning at
cpuset_attach() [1], for commit 4f7e7236435ca0ab ("cgroup: Fix
threadgroup_rwsem <-> cpus_read_lock() deadlock") missed that
cpuset_attach() is also called from cgroup_attach_task_all().
Add cpus_read_lock() like what cgroup_procs_write_start() does.

Link: https://syzkaller.appspot.com/bug?extid=29d3a3b4d86c8136ad9e [1]
Reported-by: syzbot <syzbot+29d3a3b4d86c8136ad9e@...kaller.appspotmail.com>
Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Fixes: 4f7e7236435ca0ab ("cgroup: Fix threadgroup_rwsem <-> cpus_read_lock() deadlock")
Signed-off-by: Tejun Heo <tj@...nel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 kernel/cgroup/cgroup-v1.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/kernel/cgroup/cgroup-v1.c
+++ b/kernel/cgroup/cgroup-v1.c
@@ -15,6 +15,7 @@
 #include <linux/pid_namespace.h>
 #include <linux/cgroupstats.h>
 #include <linux/fs_parser.h>
+#include <linux/cpu.h>
 
 #include <trace/events/cgroup.h>
 
@@ -62,6 +63,7 @@ int cgroup_attach_task_all(struct task_s
 	int retval = 0;
 
 	mutex_lock(&cgroup_mutex);
+	cpus_read_lock();
 	percpu_down_write(&cgroup_threadgroup_rwsem);
 	for_each_root(root) {
 		struct cgroup *from_cgrp;
@@ -78,6 +80,7 @@ int cgroup_attach_task_all(struct task_s
 			break;
 	}
 	percpu_up_write(&cgroup_threadgroup_rwsem);
+	cpus_read_unlock();
 	mutex_unlock(&cgroup_mutex);
 
 	return retval;