Consider the following scenario:
thread 1: zswap reclaim entry x (get the refcount, but not call
zswap_get_swap_cache_page yet)
thread 0: zswap_frontswap_invalidate_page entry x (finished, entry x
and its zbud is not freed as its refcount != 0)
now, the swap_map[x] = 0
thread 1: zswap_get_swap_cache_page called, 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
---
mm/zswap.c | 21 +++++++++++++--------
1 files changed, 13 insertions(+), 8 deletions(-)
diff --git a/mm/zswap.c b/mm/zswap.c
index 5f97f4f..9d34c3c 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 +401,9 @@ 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,
page is locked
+ * Returns ZSWAP_SWAPCACHE_FAIL on error
*/
static int zswap_get_swap_cache_page(swp_entry_t entry,
struct page **retpage)
@@ -475,7 +475,7 @@ 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 +529,11 @@ 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 +591,12 @@ 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;
}
--
1.7.0.4
--
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