linux-kernel - [PATCH 2/3] mm: zswap: tighten up entry invalidation

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Message-ID: <20230727162343.1415598-3-hannes@cmpxchg.org>
Date:   Thu, 27 Jul 2023 12:22:24 -0400
From:   Johannes Weiner <hannes@...xchg.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Yosry Ahmed <yosryahmed@...gle.com>, Nhat Pham <nphamcs@...il.com>,
        Domenico Cerasuolo <cerasuolodomenico@...il.com>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: [PATCH 2/3] 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.

Signed-off-by: Johannes Weiner <hannes@...xchg.org>
---
 mm/zswap.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/zswap.c b/mm/zswap.c
index e123b1c7981c..e34ac89e6098 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -402,9 +402,9 @@ 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);
 	}
 }
-- 
2.41.0