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Commit e6b81710 authored by Tejun Heo's avatar Tejun Heo
Browse files

cgroup: refactor cgroup_pidlist_find() 



Rename cgroup_pidlist_find() to cgroup_pidlist_find_create() and
separate out finding proper to cgroup_pidlist_find().  Also, move
locking to the caller.

This patch is preparation for pidlist restructure and doesn't
introduce any behavior changes.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarLi Zefan <lizefan@huawei.com>
parent 62236858

kernel/cgroup.c

+38 −27
Original line number Diff line number Diff line
@@ -3575,48 +3575,50 @@ static int cmppid(const void *a, const void *b) 
	return *(pid_t *)a - *(pid_t *)b;

}



static struct cgroup_pidlist *cgroup_pidlist_find(struct cgroup *cgrp,

						  enum cgroup_filetype type)

{

	struct cgroup_pidlist *l;

	/* don't need task_nsproxy() if we're looking at ourself */

	struct pid_namespace *ns = task_active_pid_ns(current);



	lockdep_assert_held(&cgrp->pidlist_mutex);



	list_for_each_entry(l, &cgrp->pidlists, links)

		if (l->key.type == type && l->key.ns == ns)

			return l;

	return NULL;

}



/*

 * find the appropriate pidlist for our purpose (given procs vs tasks)

 * returns with the lock on that pidlist already held, and takes care

 * of the use count, or returns NULL with no locks held if we're out of

 * memory.

 */

static struct cgroup_pidlist *cgroup_pidlist_find(struct cgroup *cgrp,

static struct cgroup_pidlist *cgroup_pidlist_find_create(struct cgroup *cgrp,

						enum cgroup_filetype type)

{

	struct cgroup_pidlist *l;

	/* don't need task_nsproxy() if we're looking at ourself */

	struct pid_namespace *ns = task_active_pid_ns(current);



	/*

	 * We can't drop the pidlist_mutex before taking the l->rwsem in case

	 * the last ref-holder is trying to remove l from the list at the same

	 * time. Holding the pidlist_mutex precludes somebody taking whichever

	 * list we find out from under us - compare release_pid_array().

	 */

	mutex_lock(&cgrp->pidlist_mutex);

	list_for_each_entry(l, &cgrp->pidlists, links) {

		if (l->key.type == type && l->key.ns == ns) {

			/* make sure l doesn't vanish out from under us */

			down_write(&l->rwsem);

			mutex_unlock(&cgrp->pidlist_mutex);

	lockdep_assert_held(&cgrp->pidlist_mutex);



	l = cgroup_pidlist_find(cgrp, type);

	if (l)

		return l;

		}

	}



	/* entry not found; create a new one */

	l = kzalloc(sizeof(struct cgroup_pidlist), GFP_KERNEL);

	if (!l) {

		mutex_unlock(&cgrp->pidlist_mutex);

	if (!l)

		return l;

	}



	init_rwsem(&l->rwsem);

	INIT_DELAYED_WORK(&l->destroy_dwork, cgroup_pidlist_destroy_work_fn);

	down_write(&l->rwsem);

	l->key.type = type;

	l->key.ns = get_pid_ns(ns);

	/* don't need task_nsproxy() if we're looking at ourself */

	l->key.ns = get_pid_ns(task_active_pid_ns(current));

	l->owner = cgrp;

	list_add(&l->links, &cgrp->pidlists);

	mutex_unlock(&cgrp->pidlist_mutex);

	return l;

}
@@ -3662,17 +3664,26 @@ static int pidlist_array_load(struct cgroup *cgrp, enum cgroup_filetype type, 
	sort(array, length, sizeof(pid_t), cmppid, NULL);

	if (type == CGROUP_FILE_PROCS)

		length = pidlist_uniq(array, length);

	l = cgroup_pidlist_find(cgrp, type);



	mutex_lock(&cgrp->pidlist_mutex);



	l = cgroup_pidlist_find_create(cgrp, type);

	if (!l) {

		mutex_unlock(&cgrp->pidlist_mutex);

		pidlist_free(array);

		return -ENOMEM;

	}

	/* store array, freeing old if necessary - lock already held */



	/* store array, freeing old if necessary */

	down_write(&l->rwsem);

	pidlist_free(l->list);

	l->list = array;

	l->length = length;

	l->use_count++;

	up_write(&l->rwsem);



	mutex_unlock(&cgrp->pidlist_mutex);



	*lp = l;

	return 0;

}