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    Subject[PATCH 3.11 204/272] mm/zswap: bugfix: memory leak when invalidate and reclaim occur concurrently
    Date
    3.11.10.1 -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: Luis Henriques <luis.henriques@canonical.com>
    ---
    mm/zswap.c | 22 ++++++++++++++--------
    1 file changed, 14 insertions(+), 8 deletions(-)

    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;
    }
    --
    1.8.3.2


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