io_uring/bpf_filter: add ref counts to struct io_bpf_filter

In preparation for allowing inheritance of BPF filters and filter
tables, add a reference count to the filter. This allows multiple tables
to safely include the same filter.

Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: axboe

io_uring/bpf_filter.c

@@ -15,6 +15,7 @@
 #include "openclose.h"
 
 struct io_bpf_filter {
+	refcount_t		refs;
 	struct bpf_prog		*prog;
 	struct io_bpf_filter	*next;
 };
@@ -125,6 +126,11 @@ static void io_free_bpf_filters(struct rcu_head *head)
 			 */
 			if (f == &dummy_filter)
 				break;
+
+			/* Someone still holds a ref, stop iterating. */
+			if (!refcount_dec_and_test(&f->refs))
+				break;
+
 			bpf_prog_destroy(f->prog);
 			kfree(f);
 			f = next;
@@ -298,6 +304,7 @@ int io_register_bpf_filter(struct io_restriction *res,
 		ret = -ENOMEM;
 		goto err;
 	}
+	refcount_set(&filter->refs, 1);
 	filter->prog = prog;
 	res->bpf_filters = filters;