From b4e6ae7ba711758c38d5eb7d5a7a0712273bdf6f Mon Sep 17 00:00:00 2001
From: Alexander Aring <aahringo@redhat.com>
Date: Tue, 1 Sep 2026 13:47:15 -0400
Subject: [PATCH] dlm: fix variable key length lookup

Before commit 6c648035cbe7 ("dlm: switch to use rhashtable for rsbs")
the rsb hashtable was dynamic key length. Accidentally it was changed to
switch to static key length which can end in different results. We
fixing this back to the original behaviour by adding the necessary
functionality to rhashtable to handle the objects and lookups as dynamic
key lengths.

Fixes: 6c648035cbe7 ("dlm: switch to use rhashtable for rsbs")
Signed-off-by: Alexander Aring <aahringo@redhat.com>
Signed-off-by: David Teigland <teigland@redhat.com>
---
 fs/dlm/config.c       | 30 ++++++++++++++++++++++++++++--
 fs/dlm/dlm_internal.h |  5 +++++
 fs/dlm/lock.c         |  6 ++++--
 3 files changed, 37 insertions(+), 4 deletions(-)

diff --git a/fs/dlm/config.c b/fs/dlm/config.c
index 53cd33293042..6c5c3f049b33 100644
--- a/fs/dlm/config.c
+++ b/fs/dlm/config.c
@@ -64,11 +64,37 @@ static void release_node(struct config_item *);
 static struct configfs_attribute *comm_attrs[];
 static struct configfs_attribute *node_attrs[];
 
+static u32 rsb_hashfn(const void *data, u32 len, u32 seed)
+{
+	const struct dlm_rsb_key *key = data;
+
+	return jhash(key->name, key->len, 0);
+}
+
+static u32 rsb_obj_hashfn(const void *data, u32 len, u32 seed)
+{
+	const struct dlm_rsb *r = data;
+
+	return r->res_hash;
+}
+
+static int rsb_obj_cmpfn(struct rhashtable_compare_arg *arg, const void *obj)
+{
+	const struct dlm_rsb_key *key = arg->key;
+	const struct dlm_rsb *r = obj;
+
+	if (key->len != r->res_length)
+		return -1;
+
+	return memcmp(&r->res_name, key->name, key->len);
+}
+
 const struct rhashtable_params dlm_rhash_rsb_params = {
 	.nelem_hint = 3, /* start small */
-	.key_len = DLM_RESNAME_MAXLEN,
-	.key_offset = offsetof(struct dlm_rsb, res_name),
 	.head_offset = offsetof(struct dlm_rsb, res_node),
+	.hashfn = rsb_hashfn,
+	.obj_hashfn = rsb_obj_hashfn,
+	.obj_cmpfn = rsb_obj_cmpfn,
 	.automatic_shrinking = true,
 };
 
diff --git a/fs/dlm/dlm_internal.h b/fs/dlm/dlm_internal.h
index 9df842421ae0..74c2e77d1b55 100644
--- a/fs/dlm/dlm_internal.h
+++ b/fs/dlm/dlm_internal.h
@@ -340,6 +340,11 @@ struct dlm_rsb {
 	char			res_name[DLM_RESNAME_MAXLEN+1];
 };
 
+struct dlm_rsb_key {
+	char name[DLM_RESNAME_MAXLEN];
+	size_t len;
+};
+
 /* dlm_master_lookup() flags */
 
 #define DLM_LU_RECOVER_DIR	1
diff --git a/fs/dlm/lock.c b/fs/dlm/lock.c
index d73c4aed1f8a..2609e4fdeba8 100644
--- a/fs/dlm/lock.c
+++ b/fs/dlm/lock.c
@@ -625,12 +625,14 @@ static int get_rsb_struct(struct dlm_ls *ls, const void *name, int len,
 int dlm_search_rsb_tree(struct rhashtable *rhash, const void *name,
 			unsigned int len, struct dlm_rsb **r_ret)
 {
-	char key[DLM_RESNAME_MAXLEN] = {};
+	struct dlm_rsb_key key = {
+		.len = len,
+	};
 
 	if (len > DLM_RESNAME_MAXLEN)
 		return -EINVAL;
 
-	memcpy(key, name, len);
+	memcpy(key.name, name, len);
 	*r_ret = rhashtable_lookup_fast(rhash, &key, dlm_rhash_rsb_params);
 	if (*r_ret)
 		return 0;