msm: kgsl: Make sure that pool pages don't have any extra references

Before putting a page back in the pool be sure that it doesn't have
any additional references that would be a signal that somebody else
is looking at the page and that it would be a bad idea to keep it
around and run the risk of accidentally handing it to a different
process.

Change-Id: Ic0dedbad0cf2ffb34b76ad23e393c5a911114b82
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>
Signed-off-by: Kamal Agrawal <quic_kamaagra@quicinc.com>

drivers/gpu/msm/kgsl_pool.c

@@ -1,4 +1,5 @@
 /* Copyright (c) 2016-2017, The Linux Foundation. All rights reserved.
+ * Copyright (c) 2023 Qualcomm Innovation Center, Inc. All rights reserved.
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 2 and
@@ -83,6 +84,15 @@ _kgsl_pool_zero_page(struct page *p, unsigned int pool_order)
 static void
 _kgsl_pool_add_page(struct kgsl_page_pool *pool, struct page *p)
 {
+	/*
+	 * Sanity check to make sure we don't re-pool a page that
+	 * somebody else has a reference to.
+	 */
+	if (WARN_ON_ONCE(unlikely(page_count(p) > 1))) {
+		__free_pages(p, pool->pool_order);
+		return;
+	}
+
 	_kgsl_pool_zero_page(p, pool->pool_order);
 
 	spin_lock(&pool->list_lock);