linux-kernel - [PATCH 3.12 083/212] mm/zswap: bugfix: memory leak when invalidate and reclaim occur concurrently

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Message-Id: <20131202191256.939611282@linuxfoundation.org>
Date:	Mon,  2 Dec 2013 11:14:34 -0800
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Weijie Yang <weijie.yang@...sung.com>,
	Bob Liu <bob.liu@...cle.com>, Minchan Kim <minchan@...nel.org>,
	Seth Jennings <sjenning@...ux.vnet.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 3.12 083/212] mm/zswap: bugfix: memory leak when invalidate and reclaim occur concurrently

3.12-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Weijie Yang <weijie.yang@...sung.com>

commit 67d13fe846c57a54d12578e7a4518f68c5c86ad7 upstream.

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: Weijie Yang <weijie.yang@...sung.com>
Reviewed-by: Bob Liu <bob.liu@...cle.com>
Reviewed-by: Minchan Kim <minchan@...nel.org>
Acked-by: Seth Jennings <sjenning@...ux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 mm/zswap.c |   22 ++++++++++++++--------
 1 file changed, 14 insertions(+), 8 deletions(-)

--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -387,7 +387,7 @@ static void zswap_free_entry(struct zswa
 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
 	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
 
 	/* 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;
@@ -591,7 +592,12 @@ static int zswap_writeback_entry(struct
 
 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;
 }


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