From af4ee5e977acb150371c28bd85cb7e34cac48b13 Mon Sep 17 00:00:00 2001 From: Minchan Kim Date: Fri, 12 Dec 2014 16:56:58 -0800 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. I got a subtle bug when I implemented a new feature of zsmalloc (compaction) due to a link's mishandling (the link was over page boundary). Although it was totally my mistake, it took a while to find the cause because an unpredictable kmapped address was unmapped causing an almost random crash. Signed-off-by: Minchan Kim Cc: Nitin Gupta Cc: Sergey Senozhatsky Cc: Dan Streetman Cc: Seth Jennings Cc: Jerome Marchand Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/zsmalloc.c | 21 ++++++++++++--------- 1 file changed, 12 insertions(+), 9 deletions(-) diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c index 5481c677e465..83ecdb675c40 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; } @@ -1064,6 +1065,7 @@ 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; @@ -1092,11 +1094,11 @@ 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 */ @@ -1112,6 +1114,7 @@ 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; @@ -1130,10 +1133,10 @@ 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--; -- 2.30.2