[PATCH bpf-next v2 1/8] xdp: simplify devmap cleanup

Björn Töpel
2019-12-19T06:10:27Z

From: Björn Töpel <bjorn.topel@intel.com>

After the RCU flavor consolidation [1], call_rcu() and
synchronize_rcu() waits for preempt-disable regions (NAPI) in addition
to the read-side critical sections. As a result of this, the cleanup
code in devmap can be simplified

* There is no longer a need to flush in __dev_map_entry_free, since we
know that this has been done when the call_rcu() callback is
triggered.

* When freeing the map, there is no need to explicitly wait for a
flush. It's guaranteed to be done after the synchronize_rcu() call
in dev_map_free(). The rcu_barrier() is still needed, so that the
map is not freed prior the elements.

[1] https://lwn.net/Articles/777036/

Acked-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
---
kernel/bpf/devmap.c | 43 +++++--------------------------------------
1 file changed, 5 insertions(+), 38 deletions(-)

diff --git a/kernel/bpf/devmap.c b/kernel/bpf/devmap.c
index 3d3d61b5985b..b7595de6a91a 100644
--- a/kernel/bpf/devmap.c
+++ b/kernel/bpf/devmap.c
@@ -201,7 +201,7 @@ static struct bpf_map *dev_map_alloc(union bpf_attr *attr)
static void dev_map_free(struct bpf_map *map)
{
struct bpf_dtab *dtab = container_of(map, struct bpf_dtab, map);
- int i, cpu;
+ int i;

/* At this point bpf_prog->aux->refcnt == 0 and this map->refcnt == 0,
* so the programs (can be more than one that used this map) were
@@ -221,18 +221,6 @@ static void dev_map_free(struct bpf_map *map)
/* Make sure prior __dev_map_entry_free() have completed. */
rcu_barrier();

- /* To ensure all pending flush operations have completed wait for flush
- * list to empty on _all_ cpus.
- * Because the above synchronize_rcu() ensures the map is disconnected
- * from the program we can assume no new items will be added.
- */
- for_each_online_cpu(cpu) {
- struct list_head *flush_list = per_cpu_ptr(dtab->flush_list, cpu);
-
- while (!list_empty(flush_list))
- cond_resched();
- }
-
if (dtab->map.map_type == BPF_MAP_TYPE_DEVMAP_HASH) {
for (i = 0; i < dtab->n_buckets; i++) {
struct bpf_dtab_netdev *dev;
@@ -345,8 +333,7 @@ static int dev_map_hash_get_next_key(struct bpf_map *map, void *key,
return -ENOENT;
}

-static int bq_xmit_all(struct xdp_bulk_queue *bq, u32 flags,
- bool in_napi_ctx)
+static int bq_xmit_all(struct xdp_bulk_queue *bq, u32 flags)
{
struct bpf_dtab_netdev *obj = bq->obj;
struct net_device *dev = obj->dev;
@@ -384,11 +371,7 @@ static int bq_xmit_all(struct xdp_bulk_queue *bq, u32 flags,
for (i = 0; i < bq->count; i++) {
struct xdp_frame *xdpf = bq->q[i];

- /* RX path under NAPI protection, can return frames faster */
- if (likely(in_napi_ctx))
- xdp_return_frame_rx_napi(xdpf);
- else
- xdp_return_frame(xdpf);
+ xdp_return_frame_rx_napi(xdpf);
drops++;
}
goto out;
@@ -409,7 +392,7 @@ void __dev_map_flush(struct bpf_map *map)

rcu_read_lock();
list_for_each_entry_safe(bq, tmp, flush_list, flush_node)
- bq_xmit_all(bq, XDP_XMIT_FLUSH, true);
+ bq_xmit_all(bq, XDP_XMIT_FLUSH);
rcu_read_unlock();
}

@@ -440,7 +423,7 @@ static int bq_enqueue(struct bpf_dtab_netdev *obj, struct xdp_frame *xdpf,
struct xdp_bulk_queue *bq = this_cpu_ptr(obj->bulkq);

if (unlikely(bq->count == DEV_MAP_BULK_SIZE))
- bq_xmit_all(bq, 0, true);
+ bq_xmit_all(bq, 0);

/* Ingress dev_rx will be the same for all xdp_frame's in
* bulk_queue, because bq stored per-CPU and must be flushed
@@ -509,27 +492,11 @@ static void *dev_map_hash_lookup_elem(struct bpf_map *map, void *key)
return dev ? &dev->ifindex : NULL;
}

-static void dev_map_flush_old(struct bpf_dtab_netdev *dev)
-{
- if (dev->dev->netdev_ops->ndo_xdp_xmit) {
- struct xdp_bulk_queue *bq;
- int cpu;
-
- rcu_read_lock();
- for_each_online_cpu(cpu) {
- bq = per_cpu_ptr(dev->bulkq, cpu);
- bq_xmit_all(bq, XDP_XMIT_FLUSH, false);
- }
- rcu_read_unlock();
- }
-}
-
static void __dev_map_entry_free(struct rcu_head *rcu)
{
struct bpf_dtab_netdev *dev;

dev = container_of(rcu, struct bpf_dtab_netdev, rcu);
- dev_map_flush_old(dev);
free_percpu(dev->bulkq);
dev_put(dev->dev);
kfree(dev);
--
2.20.1