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Commit e4463009 authored by Tejun Heo's avatar Tejun Heo Committed by Greg Kroah-Hartman
Browse files

cgroup: Fix threadgroup_rwsem <-> cpus_read_lock() deadlock 



commit 4f7e7236435ca0abe005c674ebd6892c6e83aeb3 upstream.

Add #include <linux/cpu.h> to avoid compile error on some architectures.

commit 9a3284fad42f6 ("cgroup: Optimize single thread migration") and
commit 671c11f0619e5 ("cgroup: Elide write-locking threadgroup_rwsem
when updating csses on an empty subtree") are not backport. So ignore the
input parameter of cgroup_attach_lock/cgroup_attach_unlock.

original commit message:

Bringing up a CPU may involve creating and destroying tasks which requires
read-locking threadgroup_rwsem, so threadgroup_rwsem nests inside
cpus_read_lock(). However, cpuset's ->attach(), which may be called with
thredagroup_rwsem write-locked, also wants to disable CPU hotplug and
acquires cpus_read_lock(), leading to a deadlock.

Fix it by guaranteeing that ->attach() is always called with CPU hotplug
disabled and removing cpus_read_lock() call from cpuset_attach().

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Reviewed-and-tested-by: default avatarImran Khan <imran.f.khan@oracle.com>
Reported-and-tested-by: default avatarXuewen Yan <xuewen.yan@unisoc.com>
Fixes: 05c7b7a92cc8 ("cgroup/cpuset: Fix a race between cpuset_attach() and cpu hotplug")
Cc: stable@vger.kernel.org # v5.17+
Signed-off-by: default avatarCai Xinchen <caixinchen1@huawei.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 22426258

kernel/cgroup/cgroup.c

+45 −5
Original line number Diff line number Diff line
@@ -55,6 +55,7 @@ 
#include <linux/nsproxy.h>

#include <linux/file.h>

#include <linux/sched/cputime.h>

#include <linux/cpu.h>

#include <net/sock.h>



#define CREATE_TRACE_POINTS
@@ -2209,6 +2210,45 @@ int task_cgroup_path(struct task_struct *task, char *buf, size_t buflen) 
}

EXPORT_SYMBOL_GPL(task_cgroup_path);



/**

 * cgroup_attach_lock - Lock for ->attach()

 * @lock_threadgroup: whether to down_write cgroup_threadgroup_rwsem

 *

 * cgroup migration sometimes needs to stabilize threadgroups against forks and

 * exits by write-locking cgroup_threadgroup_rwsem. However, some ->attach()

 * implementations (e.g. cpuset), also need to disable CPU hotplug.

 * Unfortunately, letting ->attach() operations acquire cpus_read_lock() can

 * lead to deadlocks.

 *

 * Bringing up a CPU may involve creating and destroying tasks which requires

 * read-locking threadgroup_rwsem, so threadgroup_rwsem nests inside

 * cpus_read_lock(). If we call an ->attach() which acquires the cpus lock while

 * write-locking threadgroup_rwsem, the locking order is reversed and we end up

 * waiting for an on-going CPU hotplug operation which in turn is waiting for

 * the threadgroup_rwsem to be released to create new tasks. For more details:

 *

 *   http://lkml.kernel.org/r/20220711174629.uehfmqegcwn2lqzu@wubuntu

 *

 * Resolve the situation by always acquiring cpus_read_lock() before optionally

 * write-locking cgroup_threadgroup_rwsem. This allows ->attach() to assume that

 * CPU hotplug is disabled on entry.

 */

static void cgroup_attach_lock(void)

{

	get_online_cpus();

	percpu_down_write(&cgroup_threadgroup_rwsem);

}



/**

 * cgroup_attach_unlock - Undo cgroup_attach_lock()

 * @lock_threadgroup: whether to up_write cgroup_threadgroup_rwsem

 */

static void cgroup_attach_unlock(void)

{

	percpu_up_write(&cgroup_threadgroup_rwsem);

	put_online_cpus();

}



/**

 * cgroup_migrate_add_task - add a migration target task to a migration context

 * @task: target task
@@ -2694,7 +2734,7 @@ struct task_struct *cgroup_procs_write_start(char *buf, bool threadgroup) 
	if (kstrtoint(strstrip(buf), 0, &pid) || pid < 0)

		return ERR_PTR(-EINVAL);



	percpu_down_write(&cgroup_threadgroup_rwsem);

	cgroup_attach_lock();



	rcu_read_lock();

	if (pid) {
@@ -2725,7 +2765,7 @@ struct task_struct *cgroup_procs_write_start(char *buf, bool threadgroup) 
	goto out_unlock_rcu;



out_unlock_threadgroup:

	percpu_up_write(&cgroup_threadgroup_rwsem);

	cgroup_attach_unlock();

out_unlock_rcu:

	rcu_read_unlock();

	return tsk;
@@ -2740,7 +2780,7 @@ void cgroup_procs_write_finish(struct task_struct *task) 
	/* release reference from cgroup_procs_write_start() */

	put_task_struct(task);



	percpu_up_write(&cgroup_threadgroup_rwsem);

	cgroup_attach_unlock();

	for_each_subsys(ss, ssid)

		if (ss->post_attach)

			ss->post_attach();
@@ -2799,7 +2839,7 @@ static int cgroup_update_dfl_csses(struct cgroup *cgrp) 


	lockdep_assert_held(&cgroup_mutex);



	percpu_down_write(&cgroup_threadgroup_rwsem);

	cgroup_attach_lock();



	/* look up all csses currently attached to @cgrp's subtree */

	spin_lock_irq(&css_set_lock);
@@ -2830,7 +2870,7 @@ static int cgroup_update_dfl_csses(struct cgroup *cgrp) 
	ret = cgroup_migrate_execute(&mgctx);

out_finish:

	cgroup_migrate_finish(&mgctx);

	percpu_up_write(&cgroup_threadgroup_rwsem);

	cgroup_attach_unlock();

	return ret;

}

kernel/cgroup/cpuset.c

+1 −6
Original line number Diff line number Diff line
@@ -1528,11 +1528,7 @@ static void cpuset_attach(struct cgroup_taskset *tset) 
	cgroup_taskset_first(tset, &css);

	cs = css_cs(css);



	/*

	 * It should hold cpus lock because a cpu offline event can

	 * cause set_cpus_allowed_ptr() failed.

	 */

	get_online_cpus();

	lockdep_assert_cpus_held();     /* see cgroup_attach_lock() */

	mutex_lock(&cpuset_mutex);



	/* prepare for attach */
@@ -1588,7 +1584,6 @@ static void cpuset_attach(struct cgroup_taskset *tset) 
		wake_up(&cpuset_attach_wq);



	mutex_unlock(&cpuset_mutex);

	put_online_cpus();

}



/* The various types of files and directories in a cpuset file system */