cgroup: use kzalloc() instead of kmalloc()

There's no point in using kmalloc() instead of the clearing variant
for trivial stuff.  We can live dangerously elsewhere.  Use kzalloc()
instead and drop 0 inits.

While at it, do trivial code reorganization in cgroup_file_open().

This patch doesn't introduce any functional changes.

v2: I was caught in the very distant past where list_del() didn't
    poison and the initial version converted list_del()s to
    list_del_init()s too.  Li and Kent took me out of the stasis
    chamber.
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Kent Overstreet <koverstreet@google.com>
Acked-by: Li Zefan <lizefan@huawei.com>

kernel/cgroup.c

@@ -597,7 +597,7 @@ static int allocate_cgrp_cset_links(int count, struct list_head *tmp_links)
 	INIT_LIST_HEAD(tmp_links);
 
 	for (i = 0; i < count; i++) {
-		link = kmalloc(sizeof(*link), GFP_KERNEL);
+		link = kzalloc(sizeof(*link), GFP_KERNEL);
 		if (!link) {
 			free_cgrp_cset_links(tmp_links);
 			return -ENOMEM;
@@ -658,7 +658,7 @@ static struct css_set *find_css_set(struct css_set *old_cset,
 	if (cset)
 		return cset;
 
-	cset = kmalloc(sizeof(*cset), GFP_KERNEL);
+	cset = kzalloc(sizeof(*cset), GFP_KERNEL);
 	if (!cset)
 		return NULL;
 
@@ -2475,10 +2475,12 @@ static int cgroup_file_open(struct inode *inode, struct file *file)
 	cft = __d_cft(file->f_dentry);
 
 	if (cft->read_map || cft->read_seq_string) {
-		struct cgroup_seqfile_state *state =
-			kzalloc(sizeof(*state), GFP_USER);
+		struct cgroup_seqfile_state *state;
+
+		state = kzalloc(sizeof(*state), GFP_USER);
 		if (!state)
 			return -ENOMEM;
+
 		state->cft = cft;
 		state->cgroup = __d_cgrp(file->f_dentry->d_parent);
 		file->f_op = &cgroup_seqfile_operations;
@@ -3511,7 +3513,7 @@ static struct cgroup_pidlist *cgroup_pidlist_find(struct cgroup *cgrp,
 		}
 	}
 	/* entry not found; create a new one */
-	l = kmalloc(sizeof(struct cgroup_pidlist), GFP_KERNEL);
+	l = kzalloc(sizeof(struct cgroup_pidlist), GFP_KERNEL);
 	if (!l) {
 		mutex_unlock(&cgrp->pidlist_mutex);
 		return l;
@@ -3520,8 +3522,6 @@ static struct cgroup_pidlist *cgroup_pidlist_find(struct cgroup *cgrp,
 	down_write(&l->mutex);
 	l->key.type = type;
 	l->key.ns = get_pid_ns(ns);
-	l->use_count = 0; /* don't increment here */
-	l->list = NULL;
 	l->owner = cgrp;
 	list_add(&l->links, &cgrp->pidlists);
 	mutex_unlock(&cgrp->pidlist_mutex);