linux-kernel - [PATCH] zsmalloc: correct fragile [kmap|kunmap]

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Message-Id: <1415927461-14220-1-git-send-email-minchan@kernel.org>
Date:	Fri, 14 Nov 2014 10:11:01 +0900
From:	Minchan Kim <minchan@...nel.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Nitin Gupta <ngupta@...are.org>,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	Dan Streetman <ddstreet@...e.org>,
	Seth Jennings <sjennings@...iantweb.net>,
	Jerome Marchand <jmarchan@...hat.com>,
	Minchan Kim <minchan@...nel.org>
Subject: [PATCH] zsmalloc: correct fragile [kmap|kunmap]_atomic use

The kunmap_atomic should use virtual address getting by kmap_atomic.
However, some pieces of code in zsmalloc uses modified address,
not the one got by kmap_atomic for kunmap_atomic.

It's okay for working because zsmalloc modifies the address
inner PAGE_SIZE bounday so it works with current kmap_atomic's
implementation. But it's still fragile with potential changing
of kmap_atomic so let's correct it.

Signed-off-by: Minchan Kim <minchan@...nel.org>
---
 mm/zsmalloc.c | 21 ++++++++++++---------
 1 file changed, 12 insertions(+), 9 deletions(-)

diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index b3b57ef85830..85e14f584048 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -629,6 +629,7 @@ static void init_zspage(struct page *first_page, struct size_class *class)
 		struct page *next_page;
 		struct link_free *link;
 		unsigned int i = 1;
+		void *vaddr;
 
 		/*
 		 * page->index stores offset of first object starting
@@ -639,8 +640,8 @@ static void init_zspage(struct page *first_page, struct size_class *class)
 		if (page != first_page)
 			page->index = off;
 
-		link = (struct link_free *)kmap_atomic(page) +
-						off / sizeof(*link);
+		vaddr = kmap_atomic(page);
+		link = (struct link_free *)vaddr + off / sizeof(*link);
 
 		while ((off += class->size) < PAGE_SIZE) {
 			link->next = obj_location_to_handle(page, i++);
@@ -654,7 +655,7 @@ static void init_zspage(struct page *first_page, struct size_class *class)
 		 */
 		next_page = get_next_page(page);
 		link->next = obj_location_to_handle(next_page, 0);
-		kunmap_atomic(link);
+		kunmap_atomic(vaddr);
 		page = next_page;
 		off %= PAGE_SIZE;
 	}
@@ -1055,6 +1056,7 @@ unsigned long zs_malloc(struct zs_pool *pool, size_t size)
 	unsigned long obj;
 	struct link_free *link;
 	struct size_class *class;
+	void *vaddr;
 
 	struct page *first_page, *m_page;
 	unsigned long m_objidx, m_offset;
@@ -1083,11 +1085,11 @@ unsigned long zs_malloc(struct zs_pool *pool, size_t size)
 	obj_handle_to_location(obj, &m_page, &m_objidx);
 	m_offset = obj_idx_to_offset(m_page, m_objidx, class->size);
 
-	link = (struct link_free *)kmap_atomic(m_page) +
-					m_offset / sizeof(*link);
+	vaddr = kmap_atomic(m_page);
+	link = (struct link_free *)vaddr + m_offset / sizeof(*link);
 	first_page->freelist = link->next;
 	memset(link, POISON_INUSE, sizeof(*link));
-	kunmap_atomic(link);
+	kunmap_atomic(vaddr);
 
 	first_page->inuse++;
 	/* Now move the zspage to another fullness group, if required */
@@ -1103,6 +1105,7 @@ void zs_free(struct zs_pool *pool, unsigned long obj)
 	struct link_free *link;
 	struct page *first_page, *f_page;
 	unsigned long f_objidx, f_offset;
+	void *vaddr;
 
 	int class_idx;
 	struct size_class *class;
@@ -1121,10 +1124,10 @@ void zs_free(struct zs_pool *pool, unsigned long obj)
 	spin_lock(&class->lock);
 
 	/* Insert this object in containing zspage's freelist */
-	link = (struct link_free *)((unsigned char *)kmap_atomic(f_page)
-							+ f_offset);
+	vaddr = kmap_atomic(f_page);
+	link = (struct link_free *)(vaddr + f_offset);
 	link->next = first_page->freelist;
-	kunmap_atomic(link);
+	kunmap_atomic(vaddr);
 	first_page->freelist = (void *)obj;
 
 	first_page->inuse--;
-- 
2.0.0

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