Commit af4ee5e9 authored by Minchan Kim's avatar Minchan Kim Committed by Linus Torvalds
Browse files

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: default avatarMinchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Dan Streetman <ddstreet@ieee.org>
Cc: Seth Jennings <sjennings@variantweb.net>
Cc: Jerome Marchand <jmarchan@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent b1b00a5b

mm/zsmalloc.c

+12 −9
Original line number Diff line number Diff line
@@ -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--;

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