bpf: consolidate bpf_prog_put{, _rcu} dismantle paths

We currently have duplicated cleanup code in bpf_prog_put() and
bpf_prog_put_rcu() cleanup paths. Back then we decided that it was
not worth it to make it a common helper called by both, but with
the recent addition of resource charging, we could have avoided
the fix in commit ac00737f4e81 ("bpf: Need to call bpf_prog_uncharge_memlock
from bpf_prog_put") if we would have had only a single, common path.
We can simplify it further by assigning aux->prog only once during
allocation time.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

kernel/bpf/core.c

@@ -92,6 +92,7 @@ struct bpf_prog *bpf_prog_alloc(unsigned int size, gfp_t gfp_extra_flags)
 
 	fp->pages = size / PAGE_SIZE;
 	fp->aux = aux;
+	fp->aux->prog = fp;
 
 	return fp;
 }
@@ -116,6 +117,7 @@ struct bpf_prog *bpf_prog_realloc(struct bpf_prog *fp_old, unsigned int size,
 
 		memcpy(fp, fp_old, fp_old->pages * PAGE_SIZE);
 		fp->pages = size / PAGE_SIZE;
+		fp->aux->prog = fp;
 
 		/* We keep fp->aux from fp_old around in the new
 		 * reallocated structure.
@@ -726,7 +728,6 @@ void bpf_prog_free(struct bpf_prog *fp)
 	struct bpf_prog_aux *aux = fp->aux;
 
 	INIT_WORK(&aux->work, bpf_prog_free_deferred);
-	aux->prog = fp;
 	schedule_work(&aux->work);
 }
 EXPORT_SYMBOL_GPL(bpf_prog_free);

kernel/bpf/syscall.c

@@ -513,7 +513,7 @@ static void bpf_prog_uncharge_memlock(struct bpf_prog *prog)
 	free_uid(user);
 }
 
-static void __prog_put_rcu(struct rcu_head *rcu)
+static void __prog_put_common(struct rcu_head *rcu)
 {
 	struct bpf_prog_aux *aux = container_of(rcu, struct bpf_prog_aux, rcu);
 
@@ -525,19 +525,14 @@ static void __prog_put_rcu(struct rcu_head *rcu)
 /* version of bpf_prog_put() that is called after a grace period */
 void bpf_prog_put_rcu(struct bpf_prog *prog)
 {
-	if (atomic_dec_and_test(&prog->aux->refcnt)) {
-		prog->aux->prog = prog;
-		call_rcu(&prog->aux->rcu, __prog_put_rcu);
-	}
+	if (atomic_dec_and_test(&prog->aux->refcnt))
+		call_rcu(&prog->aux->rcu, __prog_put_common);
 }
 
 void bpf_prog_put(struct bpf_prog *prog)
 {
-	if (atomic_dec_and_test(&prog->aux->refcnt)) {
-		free_used_maps(prog->aux);
-		bpf_prog_uncharge_memlock(prog);
-		bpf_prog_free(prog);
-	}
+	if (atomic_dec_and_test(&prog->aux->refcnt))
+		__prog_put_common(&prog->aux->rcu);
 }
 EXPORT_SYMBOL_GPL(bpf_prog_put);