From: Jakub Kicinski <jakub.kicinski@netronome.com>
Date: Wed, 27 Dec 2017 18:39:03 -0800
Subject: bpf: offload: don't require rtnl for dev list manipulation
Patch-mainline: v4.16-rc1
Git-commit: e0d3974ac77b0d581b92affe5851fc40ad2f42a4
References: bsc#1109837

We don't need the RTNL lock for all operations on offload state.
We only need to hold it around ndo calls.  The device offload
initialization doesn't require it.  The soon-to-come querying
of the offload info will only need it partially.  We will also
be able to remove the waitqueue in following patches.

Use struct rw_semaphore because map offload will require sleeping
with the semaphore held for read.

Suggested-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Quentin Monnet <quentin.monnet@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
---
 kernel/bpf/offload.c |   36 +++++++++++++++++++++++++-----------
 1 file changed, 25 insertions(+), 11 deletions(-)

--- a/kernel/bpf/offload.c
+++ b/kernel/bpf/offload.c
@@ -20,13 +20,16 @@
 #include <linux/netdevice.h>
 #include <linux/printk.h>
 #include <linux/rtnetlink.h>
+#include <linux/rwsem.h>
 
-/* protected by RTNL */
+/* Protects bpf_prog_offload_devs and offload members of all progs.
+ * RTNL lock cannot be taken when holding this lock.
+ */
+static DECLARE_RWSEM(bpf_devs_lock);
 static LIST_HEAD(bpf_prog_offload_devs);
 
 int bpf_prog_offload_init(struct bpf_prog *prog, union bpf_attr *attr)
 {
-	struct net *net = current->nsproxy->net_ns;
 	struct bpf_dev_offload *offload;
 
 	if (attr->prog_type != BPF_PROG_TYPE_SCHED_CLS &&
@@ -43,19 +46,26 @@ int bpf_prog_offload_init(struct bpf_pro
 	offload->prog = prog;
 	init_waitqueue_head(&offload->verifier_done);
 
-	rtnl_lock();
-	offload->netdev = __dev_get_by_index(net, attr->prog_ifindex);
-	if (!offload->netdev) {
-		rtnl_unlock();
-		kfree(offload);
-		return -EINVAL;
-	}
-
+	offload->netdev = dev_get_by_index(current->nsproxy->net_ns,
+					   attr->prog_ifindex);
+	if (!offload->netdev)
+		goto err_free;
+
+	down_write(&bpf_devs_lock);
+	if (offload->netdev->reg_state != NETREG_REGISTERED)
+		goto err_unlock;
 	prog->aux->offload = offload;
 	list_add_tail(&offload->offloads, &bpf_prog_offload_devs);
-	rtnl_unlock();
+	dev_put(offload->netdev);
+	up_write(&bpf_devs_lock);
 
 	return 0;
+err_unlock:
+	up_write(&bpf_devs_lock);
+	dev_put(offload->netdev);
+err_free:
+	kfree(offload);
+	return -EINVAL;
 }
 
 static int __bpf_offload_ndo(struct bpf_prog *prog, enum bpf_netdev_command cmd,
@@ -126,7 +136,9 @@ void bpf_prog_offload_destroy(struct bpf
 	wake_up(&offload->verifier_done);
 
 	rtnl_lock();
+	down_write(&bpf_devs_lock);
 	__bpf_prog_offload_destroy(prog);
+	up_write(&bpf_devs_lock);
 	rtnl_unlock();
 
 	kfree(offload);
@@ -181,11 +193,13 @@ static int bpf_offload_notification(stru
 		if (netdev->reg_state != NETREG_UNREGISTERING)
 			break;
 
+		down_write(&bpf_devs_lock);
 		list_for_each_entry_safe(offload, tmp, &bpf_prog_offload_devs,
 					 offloads) {
 			if (offload->netdev == netdev)
 				__bpf_prog_offload_destroy(offload->prog);
 		}
+		up_write(&bpf_devs_lock);
 		break;
 	default:
 		break;