Commit 265efc94 authored by Tejun Heo's avatar Tejun Heo
Browse files

Merge branch 'for-6.0-fixes' into for-6.1 

Pulling to receive 43626dad ("group: Add missing cpus_read_lock() to
cgroup_attach_task_all()") for a follow-up patch.
parents fa7e439c 43626dad

include/linux/cgroup.h

+0 −5
Original line number Diff line number Diff line
@@ -732,11 +732,6 @@ static inline struct cgroup *cgroup_parent(struct cgroup *cgrp) 
	return NULL;

}



static inline struct psi_group *cgroup_psi(struct cgroup *cgrp)

{

	return NULL;

}



static inline bool cgroup_psi_enabled(void)

{

	return false;

include/linux/psi.h

+1 −1
Original line number Diff line number Diff line
@@ -27,7 +27,7 @@ void psi_memstall_leave(unsigned long *flags); 


int psi_show(struct seq_file *s, struct psi_group *group, enum psi_res res);

struct psi_trigger *psi_trigger_create(struct psi_group *group,

			char *buf, size_t nbytes, enum psi_res res);

			char *buf, enum psi_res res);

void psi_trigger_destroy(struct psi_trigger *t);



__poll_t psi_trigger_poll(void **trigger_ptr, struct file *file,

kernel/cgroup/cgroup-v1.c

+2 −0
Original line number Diff line number Diff line
@@ -59,6 +59,7 @@ int cgroup_attach_task_all(struct task_struct *from, struct task_struct *tsk) 
	int retval = 0;



	mutex_lock(&cgroup_mutex);

	cpus_read_lock();

	percpu_down_write(&cgroup_threadgroup_rwsem);

	for_each_root(root) {

		struct cgroup *from_cgrp;
@@ -72,6 +73,7 @@ int cgroup_attach_task_all(struct task_struct *from, struct task_struct *tsk) 
			break;

	}

	percpu_up_write(&cgroup_threadgroup_rwsem);

	cpus_read_unlock();

	mutex_unlock(&cgroup_mutex);



	return retval;

kernel/cgroup/cgroup.c

+56 −24
Original line number Diff line number Diff line
@@ -1820,6 +1820,7 @@ int rebind_subsystems(struct cgroup_root *dst_root, u16 ss_mask) 


		if (ss->css_rstat_flush) {

			list_del_rcu(&css->rstat_css_node);

			synchronize_rcu();

			list_add_rcu(&css->rstat_css_node,

				     &dcgrp->rstat_css_list);

		}
@@ -2369,6 +2370,47 @@ 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(bool lock_threadgroup)

{

	cpus_read_lock();

	if (lock_threadgroup)

		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(bool lock_threadgroup)

{

	if (lock_threadgroup)

		percpu_up_write(&cgroup_threadgroup_rwsem);

	cpus_read_unlock();

}



/**

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

 * @task: target task
@@ -2841,8 +2883,7 @@ int cgroup_attach_task(struct cgroup *dst_cgrp, struct task_struct *leader, 
}



struct task_struct *cgroup_procs_write_start(char *buf, bool threadgroup,

					     bool *locked)

	__acquires(&cgroup_threadgroup_rwsem)

					     bool *threadgroup_locked)

{

	struct task_struct *tsk;

	pid_t pid;
@@ -2859,12 +2900,8 @@ struct task_struct *cgroup_procs_write_start(char *buf, bool threadgroup, 
	 * Therefore, we can skip the global lock.

	 */

	lockdep_assert_held(&cgroup_mutex);

	if (pid || threadgroup) {

		percpu_down_write(&cgroup_threadgroup_rwsem);

		*locked = true;

	} else {

		*locked = false;

	}

	*threadgroup_locked = pid || threadgroup;

	cgroup_attach_lock(*threadgroup_locked);



	rcu_read_lock();

	if (pid) {
@@ -2895,17 +2932,14 @@ struct task_struct *cgroup_procs_write_start(char *buf, bool threadgroup, 
	goto out_unlock_rcu;



out_unlock_threadgroup:

	if (*locked) {

		percpu_up_write(&cgroup_threadgroup_rwsem);

		*locked = false;

	}

	cgroup_attach_unlock(*threadgroup_locked);

	*threadgroup_locked = false;

out_unlock_rcu:

	rcu_read_unlock();

	return tsk;

}



void cgroup_procs_write_finish(struct task_struct *task, bool locked)

	__releases(&cgroup_threadgroup_rwsem)

void cgroup_procs_write_finish(struct task_struct *task, bool threadgroup_locked)

{

	struct cgroup_subsys *ss;

	int ssid;
@@ -2913,8 +2947,8 @@ void cgroup_procs_write_finish(struct task_struct *task, bool locked) 
	/* release reference from cgroup_procs_write_start() */

	put_task_struct(task);



	if (locked)

		percpu_up_write(&cgroup_threadgroup_rwsem);

	cgroup_attach_unlock(threadgroup_locked);



	for_each_subsys(ss, ssid)

		if (ss->post_attach)

			ss->post_attach();
@@ -3000,8 +3034,7 @@ static int cgroup_update_dfl_csses(struct cgroup *cgrp) 
	 * write-locking can be skipped safely.

	 */

	has_tasks = !list_empty(&mgctx.preloaded_src_csets);

	if (has_tasks)

		percpu_down_write(&cgroup_threadgroup_rwsem);

	cgroup_attach_lock(has_tasks);



	/* NULL dst indicates self on default hierarchy */

	ret = cgroup_migrate_prepare_dst(&mgctx);
@@ -3022,8 +3055,7 @@ static int cgroup_update_dfl_csses(struct cgroup *cgrp) 
	ret = cgroup_migrate_execute(&mgctx);

out_finish:

	cgroup_migrate_finish(&mgctx);

	if (has_tasks)

		percpu_up_write(&cgroup_threadgroup_rwsem);

	cgroup_attach_unlock(has_tasks);

	return ret;

}
@@ -3698,7 +3730,7 @@ static ssize_t cgroup_pressure_write(struct kernfs_open_file *of, char *buf, 
	}



	psi = cgroup_ino(cgrp) == 1 ? &psi_system : cgrp->psi;

	new = psi_trigger_create(psi, buf, nbytes, res);

	new = psi_trigger_create(psi, buf, res);

	if (IS_ERR(new)) {

		cgroup_put(cgrp);

		return PTR_ERR(new);
@@ -4971,13 +5003,13 @@ static ssize_t __cgroup_procs_write(struct kernfs_open_file *of, char *buf, 
	struct task_struct *task;

	const struct cred *saved_cred;

	ssize_t ret;

	bool locked;

	bool threadgroup_locked;



	dst_cgrp = cgroup_kn_lock_live(of->kn, false);

	if (!dst_cgrp)

		return -ENODEV;



	task = cgroup_procs_write_start(buf, threadgroup, &locked);

	task = cgroup_procs_write_start(buf, threadgroup, &threadgroup_locked);

	ret = PTR_ERR_OR_ZERO(task);

	if (ret)

		goto out_unlock;
@@ -5003,7 +5035,7 @@ static ssize_t __cgroup_procs_write(struct kernfs_open_file *of, char *buf, 
	ret = cgroup_attach_task(dst_cgrp, task, threadgroup);



out_finish:

	cgroup_procs_write_finish(task, locked);

	cgroup_procs_write_finish(task, threadgroup_locked);

out_unlock:

	cgroup_kn_unlock(of->kn);

kernel/cgroup/cpuset.c

+1 −2
Original line number Diff line number Diff line
@@ -2289,7 +2289,7 @@ static void cpuset_attach(struct cgroup_taskset *tset) 
	cgroup_taskset_first(tset, &css);

	cs = css_cs(css);



	cpus_read_lock();

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

	percpu_down_write(&cpuset_rwsem);



	guarantee_online_mems(cs, &cpuset_attach_nodemask_to);
@@ -2343,7 +2343,6 @@ static void cpuset_attach(struct cgroup_taskset *tset) 
		wake_up(&cpuset_attach_wq);



	percpu_up_write(&cpuset_rwsem);

	cpus_read_unlock();

}



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