bpf: Use __llist_del_all() whenever possbile during memory draining

Except for waiting_for_gp list, there are no concurrent operations on
free_by_rcu, free_llist and free_llist_extra lists, so use
__llist_del_all() instead of llist_del_all(). waiting_for_gp list can be
deleted by RCU callback concurrently, so still use llist_del_all().

Acked-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Hou Tao <houtao1@huawei.com>
Link: https://lore.kernel.org/r/20221021114913.60508-3-houtao@huaweicloud.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/kernel/bpf/memalloc.c b/kernel/bpf/memalloc.c
index 1cb2432..4901fa1 100644 (file)
--- a/kernel/bpf/memalloc.c
+++ b/kernel/bpf/memalloc.c
@@ -418,14 +418,17 @@ static void drain_mem_cache(struct bpf_mem_cache *c)
        /* No progs are using this bpf_mem_cache, but htab_map_free() called
         * bpf_mem_cache_free() for all remaining elements and they can be in
         * free_by_rcu or in waiting_for_gp lists, so drain those lists now.
+        *
+        * Except for waiting_for_gp list, there are no concurrent operations
+        * on these lists, so it is safe to use __llist_del_all().
         */
        llist_for_each_safe(llnode, t, __llist_del_all(&c->free_by_rcu))
                free_one(c, llnode);
        llist_for_each_safe(llnode, t, llist_del_all(&c->waiting_for_gp))
                free_one(c, llnode);
-       llist_for_each_safe(llnode, t, llist_del_all(&c->free_llist))
+       llist_for_each_safe(llnode, t, __llist_del_all(&c->free_llist))
                free_one(c, llnode);
-       llist_for_each_safe(llnode, t, llist_del_all(&c->free_llist_extra))
+       llist_for_each_safe(llnode, t, __llist_del_all(&c->free_llist_extra))
                free_one(c, llnode);
 }