Patchwork [3.11.y.z,extended,stable] Patch "mm/zswap: bugfix: memory leak when invalidate and reclaim occur" has been added to staging queue

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Submitter Luis Henriques
Date Dec. 5, 2013, 11:25 a.m.
Message ID <1386242726-3281-1-git-send-email-luis.henriques@canonical.com>
Download mbox | patch
Permalink /patch/297064/
State New
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Luis Henriques - Dec. 5, 2013, 11:25 a.m.
This is a note to let you know that I have just added a patch titled

    mm/zswap: bugfix: memory leak when invalidate and reclaim occur

to the linux-3.11.y-queue branch of the 3.11.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.11.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.11.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

From 5840836eab314630a59b5c024e1c1d95ba507c21 Mon Sep 17 00:00:00 2001
From: Weijie Yang <weijie.yang@samsung.com>
Date: Tue, 12 Nov 2013 15:08:26 -0800
Subject: mm/zswap: bugfix: memory leak when invalidate and reclaim occur
 concurrently

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@samsung.com>
Reviewed-by: Bob Liu <bob.liu@oracle.com>
Reviewed-by: Minchan Kim <minchan@kernel.org>
Acked-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
---
 mm/zswap.c | 22 ++++++++++++++--------
 1 file changed, 14 insertions(+), 8 deletions(-)

--
1.8.3.2

Patch

diff --git a/mm/zswap.c b/mm/zswap.c
index cbd9578..37d189c 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -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;
@@ -591,7 +592,12 @@  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;
 }