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cgroup: Fix threadgroup_rwsem <-> cpus_read_lock() deadlock

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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: Tejun Heo <tj@kernel.org>
Reviewed-and-tested-by: Imran Khan <imran.f.khan@oracle.com>
Reported-and-tested-by: Xuewen 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: Cai Xinchen <caixinchen1@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Tejun Heo 2023-03-20 01:15:06 +00:00 committed by Greg Kroah-Hartman
parent 224262583f
commit e446300968
2 changed files with 46 additions and 11 deletions
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50
kernel/cgroup/cgroup.c
View File

@ -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;
}

7
kernel/cgroup/cpuset.c
View File

@ -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 */