cgroup: Allocate cgroup_file_ctx for kernfs_open_file->priv

of->priv is currently used by each interface file implementation to store
private information. This patch collects the current two private data usages
into struct cgroup_file_ctx which is allocated and freed by the common path.
This allows generic private data which applies to multiple files, which will
be used to in the following patch.

Note that cgroup_procs iterator is now embedded as procs.iter in the new
cgroup_file_ctx so that it doesn't need to be allocated and freed
separately.

v2: union dropped from cgroup_file_ctx and the procs iterator is embedded in
    cgroup_file_ctx as suggested by Linus.

v3: Michal pointed out that cgroup1's procs pidlist uses of->priv too.
    Converted. Didn't change to embedded allocation as cgroup1 pidlists get
    stored for caching.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Reviewed-by: Michal Koutný <mkoutny@suse.com>

1 files changed, 14 insertions, 12 deletions

diff --git a/kernel/cgroup/cgroup-v1.c b/kernel/cgroup/cgroup-v1.c
index 0e7369103ba6..41e0837a5a0b 100644
--- a/kernel/cgroup/cgroup-v1.c
+++ b/kernel/cgroup/cgroup-v1.c
@@ -394,6 +394,7 @@ static void *cgroup_pidlist_start(struct seq_file *s, loff_t *pos)
 	 * next pid to display, if any
 	 */
 	struct kernfs_open_file *of = s->private;
+	struct cgroup_file_ctx *ctx = of->priv;
 	struct cgroup *cgrp = seq_css(s)->cgroup;
 	struct cgroup_pidlist *l;
 	enum cgroup_filetype type = seq_cft(s)->private;
@@ -403,25 +404,24 @@ static void *cgroup_pidlist_start(struct seq_file *s, loff_t *pos)
 	mutex_lock(&cgrp->pidlist_mutex);
 
 	/*
-	 * !NULL @of->priv indicates that this isn't the first start()
-	 * after open.  If the matching pidlist is around, we can use that.
-	 * Look for it.  Note that @of->priv can't be used directly.  It
-	 * could already have been destroyed.
+	 * !NULL @ctx->procs1.pidlist indicates that this isn't the first
+	 * start() after open. If the matching pidlist is around, we can use
+	 * that. Look for it. Note that @ctx->procs1.pidlist can't be used
+	 * directly. It could already have been destroyed.
 	 */
-	if (of->priv)
-		of->priv = cgroup_pidlist_find(cgrp, type);
+	if (ctx->procs1.pidlist)
+		ctx->procs1.pidlist = cgroup_pidlist_find(cgrp, type);
 
 	/*
 	 * Either this is the first start() after open or the matching
 	 * pidlist has been destroyed inbetween.  Create a new one.
 	 */
-	if (!of->priv) {
-		ret = pidlist_array_load(cgrp, type,
-					 (struct cgroup_pidlist **)&of->priv);
+	if (!ctx->procs1.pidlist) {
+		ret = pidlist_array_load(cgrp, type, &ctx->procs1.pidlist);
 		if (ret)
 			return ERR_PTR(ret);
 	}
-	l = of->priv;
+	l = ctx->procs1.pidlist;
 
 	if (pid) {
 		int end = l->length;
@@ -449,7 +449,8 @@ static void *cgroup_pidlist_start(struct seq_file *s, loff_t *pos)
 static void cgroup_pidlist_stop(struct seq_file *s, void *v)
 {
 	struct kernfs_open_file *of = s->private;
-	struct cgroup_pidlist *l = of->priv;
+	struct cgroup_file_ctx *ctx = of->priv;
+	struct cgroup_pidlist *l = ctx->procs1.pidlist;
 
 	if (l)
 		mod_delayed_work(cgroup_pidlist_destroy_wq, &l->destroy_dwork,
@@ -460,7 +461,8 @@ static void cgroup_pidlist_stop(struct seq_file *s, void *v)
 static void *cgroup_pidlist_next(struct seq_file *s, void *v, loff_t *pos)
 {
 	struct kernfs_open_file *of = s->private;
-	struct cgroup_pidlist *l = of->priv;
+	struct cgroup_file_ctx *ctx = of->priv;
+	struct cgroup_pidlist *l = ctx->procs1.pidlist;
 	pid_t *p = v;
 	pid_t *end = l->list + l->length;
 	/*