mm: zswap: tighten up entry invalidation

Removing a zswap entry from the tree is tied to an explicit operation
that's supposed to drop the base reference: swap invalidation, exclusive
load, duplicate store.  Don't silently remove the entry on final put, but
instead warn if an entry is in tree without reference.

While in that diff context, convert a BUG_ON to a WARN_ON_ONCE.  No need
to crash on a refcount underflow.

Link: https://lkml.kernel.org/r/20230727162343.1415598-3-hannes@cmpxchg.org
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Yosry Ahmed <yosryahmed@google.com>
Cc: Barry Song <song.bao.hua@hisilicon.com>
Cc: Domenico Cerasuolo <cerasuolodomenico@gmail.com>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Seth Jennings <sjenning@redhat.com>
Cc: Vitaly Wool <vitaly.wool@konsulko.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/zswap.c b/mm/zswap.c
index 93707a1799b8a51233f96acfef739c3bc3c47e54..ea921b25c245b5b1497c949b817e777158d85d86 100644 (file)
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -417,9 +417,9 @@ static void zswap_entry_put(struct zswap_tree *tree,
 {
        int refcount = --entry->refcount;
 
-       BUG_ON(refcount < 0);
+       WARN_ON_ONCE(refcount < 0);
        if (refcount == 0) {
-               zswap_rb_erase(&tree->rbroot, entry);
+               WARN_ON_ONCE(!RB_EMPTY_NODE(&entry->rbnode));
                zswap_free_entry(entry);
        }
 }