From: Hui Zhu <zhuhui@xiaomi.com>
Date: Sat, 7 Nov 2015 00:29:26 +0000 (-0800)
Subject: zsmalloc: fix obj_to_head use page_private(page) as value but not pointer
X-Git-Tag: v4.9.8~3239^2~74
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=12a7bfad58cd604616dd5205efa6dc2be6f299eb;p=platform%2Fkernel%2Flinux-rpi3.git

zsmalloc: fix obj_to_head use page_private(page) as value but not pointer

In obj_malloc():

	if (!class->huge)
		/* record handle in the header of allocated chunk */
		link->handle = handle;
	else
		/* record handle in first_page->private */
		set_page_private(first_page, handle);

In the hugepage we save handle to private directly.

But in obj_to_head():

	if (class->huge) {
		VM_BUG_ON(!is_first_page(page));
		return *(unsigned long *)page_private(page);
	} else
		return *(unsigned long *)obj;

It is used as a pointer.

The reason why there is no problem until now is huge-class page is born
with ZS_FULL so it can't be migrated.  However, we need this patch for
future work: "VM-aware zsmalloced page migration" to reduce external
fragmentation.

Signed-off-by: Hui Zhu <zhuhui@xiaomi.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---

diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index 4396b82..1fe9928 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -825,7 +825,7 @@ static unsigned long obj_to_head(struct size_class *class, struct page *page,
 {
 	if (class->huge) {
 		VM_BUG_ON(!is_first_page(page));
-		return *(unsigned long *)page_private(page);
+		return page_private(page);
 	} else
 		return *(unsigned long *)obj;
 }