[PATCH] zsmalloc: correct fragile [kmap|kunmap]_atomic use

Minchan Kim
2014-11-14T01:10:53Z

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@kernel.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