bpf: Prepare bpf_mem_alloc to be used by sleepable bpf programs.

Use call_rcu_tasks_trace() to wait for sleepable progs to finish.
Then use call_rcu() to wait for normal progs to finish
and finally do free_one() on each element when freeing objects
into global memory pool.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20220902211058.60789-14-alexei.starovoitov@gmail.com

diff --git a/kernel/bpf/memalloc.c b/kernel/bpf/memalloc.c
index f7b0778..8895c01 100644 (file)
--- a/kernel/bpf/memalloc.c
+++ b/kernel/bpf/memalloc.c
@@ -230,6 +230,13 @@ static void __free_rcu(struct rcu_head *head)
        atomic_set(&c->call_rcu_in_progress, 0);
 }
 
+static void __free_rcu_tasks_trace(struct rcu_head *head)
+{
+       struct bpf_mem_cache *c = container_of(head, struct bpf_mem_cache, rcu);
+
+       call_rcu(&c->rcu, __free_rcu);
+}
+
 static void enque_to_free(struct bpf_mem_cache *c, void *obj)
 {
        struct llist_node *llnode = obj;
@@ -255,7 +262,11 @@ static void do_call_rcu(struct bpf_mem_cache *c)
                 * from __free_rcu() and from drain_mem_cache().
                 */
                __llist_add(llnode, &c->waiting_for_gp);
-       call_rcu(&c->rcu, __free_rcu);
+       /* Use call_rcu_tasks_trace() to wait for sleepable progs to finish.
+        * Then use call_rcu() to wait for normal progs to finish
+        * and finally do free_one() on each element.
+        */
+       call_rcu_tasks_trace(&c->rcu, __free_rcu_tasks_trace);
 }
 
 static void free_bulk(struct bpf_mem_cache *c)
@@ -457,6 +468,7 @@ void bpf_mem_alloc_destroy(struct bpf_mem_alloc *ma)
                /* c->waiting_for_gp list was drained, but __free_rcu might
                 * still execute. Wait for it now before we free 'c'.
                 */
+               rcu_barrier_tasks_trace();
                rcu_barrier();
                free_percpu(ma->cache);
                ma->cache = NULL;
@@ -471,6 +483,7 @@ void bpf_mem_alloc_destroy(struct bpf_mem_alloc *ma)
                }
                if (c->objcg)
                        obj_cgroup_put(c->objcg);
+               rcu_barrier_tasks_trace();
                rcu_barrier();
                free_percpu(ma->caches);
                ma->caches = NULL;