From f7128f0f8f4430af8a6d47ea897d98eb4cf0d46f Mon Sep 17 00:00:00 2001
From: Matthew Wilcox <willy@infradead.org>
Date: Fri, 26 Oct 2018 23:24:58 -0400
Subject: [PATCH] cgroup: Convert cgroup_idr to XArray

Signed-off-by: Matthew Wilcox <willy@infradead.org>
---
 include/linux/cgroup-defs.h |  4 ++--
 kernel/cgroup/cgroup.c      | 33 ++++++++++++++-------------------
 2 files changed, 16 insertions(+), 21 deletions(-)

diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h
index 430e219e3aba..341d062905be 100644
--- a/include/linux/cgroup-defs.h
+++ b/include/linux/cgroup-defs.h
@@ -355,7 +355,7 @@ struct cgroup {
 	unsigned long flags;		/* "unsigned long" so bitops work */
 
 	/*
-	 * idr allocated in-hierarchy ID.
+	 * In-hierarchy ID.
 	 *
 	 * ID 0 is not used, the ID of the root cgroup is always 1, and a
 	 * new cgroup will be assigned with a smallest available ID.
@@ -521,7 +521,7 @@ struct cgroup_root {
 	unsigned int flags;
 
 	/* IDs for cgroups in this hierarchy */
-	struct idr cgroup_idr;
+	struct xarray cgroup_ids;
 
 	/* The path to use for release notifications. */
 	char release_agent_path[PATH_MAX];
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 753afbca549f..bc9c8fd63d8d 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -90,7 +90,7 @@ char trace_cgroup_path[TRACE_CGROUP_PATH_LEN];
 bool cgroup_debug __read_mostly;
 
 /*
- * Protects cgroup_idr and css_idr so that IDs can be released without
+ * Protects css_idr so that IDs can be released without
  * grabbing cgroup_mutex.
  */
 static DEFINE_SPINLOCK(cgroup_idr_lock);
@@ -1309,10 +1309,7 @@ static void cgroup_exit_root_id(struct cgroup_root *root)
 
 void cgroup_free_root(struct cgroup_root *root)
 {
-	if (root) {
-		idr_destroy(&root->cgroup_idr);
-		kfree(root);
-	}
+	kfree(root);
 }
 
 static void cgroup_destroy_root(struct cgroup_root *root)
@@ -1976,7 +1973,7 @@ void init_cgroup_root(struct cgroup_fs_context *ctx)
 	atomic_set(&root->nr_cgrps, 1);
 	cgrp->root = root;
 	init_cgroup_housekeeping(cgrp);
-	idr_init(&root->cgroup_idr);
+	xa_init_flags(&root->cgroup_ids, XA_FLAGS_ALLOC1 | XA_FLAGS_LOCK_BH);
 
 	root->flags = ctx->flags;
 	if (ctx->release_agent)
@@ -1997,10 +1994,10 @@ int cgroup_setup_root(struct cgroup_root *root, u16 ss_mask)
 
 	lockdep_assert_held(&cgroup_mutex);
 
-	ret = cgroup_idr_alloc(&root->cgroup_idr, root_cgrp, 1, 2, GFP_KERNEL);
+	ret = xa_insert_bh(&root->cgroup_ids, 1, root_cgrp, GFP_KERNEL);
 	if (ret < 0)
 		goto out;
-	root_cgrp->id = ret;
+	root_cgrp->id = 1;
 	root_cgrp->ancestor_ids[0] = ret;
 
 	ret = percpu_ref_init(&root_cgrp->self.refcnt, css_release,
@@ -5036,7 +5033,7 @@ static void css_release_work_fn(struct work_struct *work)
 			tcgrp->nr_dying_descendants--;
 		spin_unlock_irq(&css_set_lock);
 
-		cgroup_idr_remove(&cgrp->root->cgroup_idr, cgrp->id);
+		xa_erase_bh(&cgrp->root->cgroup_ids, cgrp->id);
 		cgrp->id = -1;
 
 		/*
@@ -5226,12 +5223,10 @@ static struct cgroup *cgroup_create(struct cgroup *parent)
 			goto out_cancel_ref;
 	}
 
-	/*
-	 * Temporarily set the pointer to NULL, so idr_find() won't return
-	 * a half-baked cgroup.
-	 */
-	cgrp->id = cgroup_idr_alloc(&root->cgroup_idr, NULL, 2, 0, GFP_KERNEL);
-	if (cgrp->id < 0) {
+	/* Use a NULL pointer, so we won't find a half-baked cgroup. */
+	ret = xa_alloc_bh(&root->cgroup_ids, &cgrp->id, NULL, xa_limit_32b,
+			GFP_KERNEL);
+	if (ret < 0) {
 		ret = -ENOMEM;
 		goto out_stat_exit;
 	}
@@ -5244,7 +5239,7 @@ static struct cgroup *cgroup_create(struct cgroup *parent)
 
 	ret = psi_cgroup_alloc(cgrp);
 	if (ret)
-		goto out_idr_free;
+		goto out_xa_free;
 
 	ret = cgroup_bpf_inherit(cgrp);
 	if (ret)
@@ -5293,7 +5288,7 @@ static struct cgroup *cgroup_create(struct cgroup *parent)
 	 * @cgrp is now fully operational.  If something fails after this
 	 * point, it'll be released via the normal destruction path.
 	 */
-	cgroup_idr_replace(&root->cgroup_idr, cgrp, cgrp->id);
+	xa_store_bh(&root->cgroup_ids, cgrp->id, cgrp, 0);
 
 	/*
 	 * On the default hierarchy, a child doesn't automatically inherit
@@ -5308,8 +5303,8 @@ static struct cgroup *cgroup_create(struct cgroup *parent)
 
 out_psi_free:
 	psi_cgroup_free(cgrp);
-out_idr_free:
-	cgroup_idr_remove(&root->cgroup_idr, cgrp->id);
+out_xa_free:
+	xa_erase_bh(&root->cgroup_ids, cgrp->id);
 out_stat_exit:
 	if (cgroup_on_dfl(parent))
 		cgroup_rstat_exit(cgrp);
-- 
2.50.1