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Subject[PATCH 3.12 083/212] mm/zswap: bugfix: memory leak when invalidate and reclaim occur concurrently
Date
3.12-stable review patch.  If anyone has any objections, please let me know.

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

From: Weijie Yang <weijie.yang@samsung.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@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: Greg Kroah-Hartman <gregkh@linuxfoundation.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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