bpf: Don't allocate per-cpu extra_elems for fd htab

JIRA: https://issues.redhat.com/browse/RHEL-78203

commit 6704b1e
Author: Hou Tao <[email protected]>
Date:   Tue Apr 1 14:22:49 2025 +0800

    bpf: Don't allocate per-cpu extra_elems for fd htab
    
    The update of element in fd htab is in-place now, therefore, there is no
    need to allocate per-cpu extra_elems, just remove it.
    
    Acked-by: Andrii Nakryiko <[email protected]>
    Signed-off-by: Hou Tao <[email protected]>
    Link: https://lore.kernel.org/r/[email protected]
    Signed-off-by: Alexei Starovoitov <[email protected]>

Signed-off-by: Viktor Malik <[email protected]>

Author: viktormalik

kernel/bpf/hashtab.c

@@ -206,9 +206,13 @@ static struct htab_elem *get_htab_elem(struct bpf_htab *htab, int i)
 	return (struct htab_elem *) (htab->elems + i * (u64)htab->elem_size);
 }
 
+/* Both percpu and fd htab support in-place update, so no need for
+ * extra elem. LRU itself can remove the least used element, so
+ * there is no need for an extra elem during map_update.
+ */
 static bool htab_has_extra_elems(struct bpf_htab *htab)
 {
-	return !htab_is_percpu(htab) && !htab_is_lru(htab);
+	return !htab_is_percpu(htab) && !htab_is_lru(htab) && !is_fd_htab(htab);
 }
 
 static void htab_free_prealloced_timers_and_wq(struct bpf_htab *htab)
@@ -464,8 +468,6 @@ static struct bpf_map *htab_map_alloc(union bpf_attr *attr)
 {
 	bool percpu = (attr->map_type == BPF_MAP_TYPE_PERCPU_HASH ||
 		       attr->map_type == BPF_MAP_TYPE_LRU_PERCPU_HASH);
-	bool lru = (attr->map_type == BPF_MAP_TYPE_LRU_HASH ||
-		    attr->map_type == BPF_MAP_TYPE_LRU_PERCPU_HASH);
 	/* percpu_lru means each cpu has its own LRU list.
 	 * it is different from BPF_MAP_TYPE_PERCPU_HASH where
 	 * the map's value itself is percpu.  percpu_lru has
@@ -560,10 +562,7 @@ static struct bpf_map *htab_map_alloc(union bpf_attr *attr)
 		if (err)
 			goto free_map_locked;
 
-		if (!percpu && !lru) {
-			/* lru itself can remove the least used element, so
-			 * there is no need for an extra elem during map_update.
-			 */
+		if (htab_has_extra_elems(htab)) {
 			err = alloc_extra_elems(htab);
 			if (err)
 				goto free_prealloc;