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Commit 67d13fe8 authored by Weijie Yang's avatar Weijie Yang Committed by Linus Torvalds
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mm/zswap: bugfix: memory leak when invalidate and reclaim occur concurrently 



Consider the following scenario:

thread 0: reclaim entry x (get refcount, but not call zswap_get_swap_cache_page)
thread 1: call zswap_frontswap_invalidate_page to invalidate entry x.
	finished, entry x and its zbud is not freed as its refcount != 0
	now, the swap_map[x] = 0
thread 0: now call zswap_get_swap_cache_page
	swapcache_prepare return -ENOENT because entry x is not used any more
	zswap_get_swap_cache_page return ZSWAP_SWAPCACHE_NOMEM
	zswap_writeback_entry do nothing except put refcount

Now, the memory of zswap_entry x and its zpage leak.

Modify:
 - check the refcount in fail path, free memory if it is not referenced.

 - use ZSWAP_SWAPCACHE_FAIL instead of ZSWAP_SWAPCACHE_NOMEM as the fail path
   can be not only caused by nomem but also by invalidate.

Signed-off-by: default avatarWeijie Yang <weijie.yang@samsung.com>
Reviewed-by: default avatarBob Liu <bob.liu@oracle.com>
Reviewed-by: default avatarMinchan Kim <minchan@kernel.org>
Acked-by: default avatarSeth Jennings <sjenning@linux.vnet.ibm.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 7a67d7ab

mm/zswap.c

+14 −8
Original line number Diff line number Diff line
@@ -387,7 +387,7 @@ static void zswap_free_entry(struct zswap_tree *tree, struct zswap_entry *entry) 
enum zswap_get_swap_ret {

	ZSWAP_SWAPCACHE_NEW,

	ZSWAP_SWAPCACHE_EXIST,

	ZSWAP_SWAPCACHE_NOMEM

	ZSWAP_SWAPCACHE_FAIL,

};



/*
@@ -401,9 +401,10 @@ enum zswap_get_swap_ret { 
 * added to the swap cache, and returned in retpage.

 *

 * If success, the swap cache page is returned in retpage

 * Returns 0 if page was already in the swap cache, page is not locked

 * Returns 1 if the new page needs to be populated, page is locked

 * Returns <0 on error

 * Returns ZSWAP_SWAPCACHE_EXIST if page was already in the swap cache

 * Returns ZSWAP_SWAPCACHE_NEW if the new page needs to be populated,

 *     the new page is added to swapcache and locked

 * Returns ZSWAP_SWAPCACHE_FAIL on error

 */

static int zswap_get_swap_cache_page(swp_entry_t entry,

				struct page **retpage)
@@ -475,7 +476,7 @@ static int zswap_get_swap_cache_page(swp_entry_t entry, 
	if (new_page)

		page_cache_release(new_page);

	if (!found_page)

		return ZSWAP_SWAPCACHE_NOMEM;

		return ZSWAP_SWAPCACHE_FAIL;

	*retpage = found_page;

	return ZSWAP_SWAPCACHE_EXIST;

}
@@ -529,11 +530,11 @@ static int zswap_writeback_entry(struct zbud_pool *pool, unsigned long handle) 


	/* try to allocate swap cache page */

	switch (zswap_get_swap_cache_page(swpentry, &page)) {

	case ZSWAP_SWAPCACHE_NOMEM: /* no memory */

	case ZSWAP_SWAPCACHE_FAIL: /* no memory or invalidate happened */

		ret = -ENOMEM;

		goto fail;



	case ZSWAP_SWAPCACHE_EXIST: /* page is unlocked */

	case ZSWAP_SWAPCACHE_EXIST:

		/* page is already in the swap cache, ignore for now */

		page_cache_release(page);

		ret = -EEXIST;
@@ -594,7 +595,12 @@ static int zswap_writeback_entry(struct zbud_pool *pool, unsigned long handle) 


fail:

	spin_lock(&tree->lock);

	zswap_entry_put(entry);

	refcount = zswap_entry_put(entry);

	if (refcount <= 0) {

		/* invalidate happened, consider writeback as success */

		zswap_free_entry(tree, entry);

		ret = 0;

	}

	spin_unlock(&tree->lock);

	return ret;

}