Merge git://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next

Daniel Borkmann says:

====================
pull-request: bpf-next 2020-01-27

The following pull-request contains BPF updates for your *net-next* tree.

We've added 20 non-merge commits during the last 5 day(s) which contain
a total of 24 files changed, 433 insertions(+), 104 deletions(-).

The main changes are:

1) Make BPF trampolines and dispatcher aware for the stack unwinder, from Jiri Olsa.

2) Improve handling of failed CO-RE relocations in libbpf, from Andrii Nakryiko.

3) Several fixes to BPF sockmap and reuseport selftests, from Lorenz Bauer.

4) Various cleanups in BPF devmap's XDP flush code, from John Fastabend.

5) Fix BPF flow dissector when used with port ranges, from Yoshiki Komachi.

6) Fix bpffs' map_seq_next callback to always inc position index, from Vasily Averin.

7) Allow overriding LLVM tooling for runqslower utility, from Andrey Ignatov.

8) Silence false-positive lockdep splats in devmap hash lookup, from Amol Grover.

9) Fix fentry/fexit selftests to initialize a variable before use, from John Sperbeck.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 16 insertions, 13 deletions

diff --git a/kernel/bpf/devmap.c b/kernel/bpf/devmap.c
index de630f980282..58bdca5d978a 100644
--- a/kernel/bpf/devmap.c
+++ b/kernel/bpf/devmap.c
@@ -190,10 +190,12 @@ static void dev_map_free(struct bpf_map *map)
 
 	/* 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
-	 * disconnected from events. Wait for outstanding critical sections in
-	 * these programs to complete. The rcu critical section only guarantees
-	 * no further reads against netdev_map. It does __not__ ensure pending
-	 * flush operations (if any) are complete.
+	 * disconnected from events. The following synchronize_rcu() guarantees
+	 * both rcu read critical sections complete and waits for
+	 * preempt-disable regions (NAPI being the relevant context here) so we
+	 * are certain there will be no further reads against the netdev_map and
+	 * all flush operations are complete. Flush operations can only be done
+	 * from NAPI context for this reason.
 	 */
 
 	spin_lock(&dev_map_lock);
@@ -263,7 +265,8 @@ struct bpf_dtab_netdev *__dev_map_hash_lookup_elem(struct bpf_map *map, u32 key)
 	struct hlist_head *head = dev_map_index_hash(dtab, key);
 	struct bpf_dtab_netdev *dev;
 
-	hlist_for_each_entry_rcu(dev, head, index_hlist)
+	hlist_for_each_entry_rcu(dev, head, index_hlist,
+				 lockdep_is_held(&dtab->index_lock))
 		if (dev->idx == key)
 			return dev;
 
@@ -363,16 +366,17 @@ error:
  * from NET_RX_SOFTIRQ. Either way the poll routine must complete before the
  * net device can be torn down. On devmap tear down we ensure the flush list
  * is empty before completing to ensure all flush operations have completed.
+ * When drivers update the bpf program they may need to ensure any flush ops
+ * are also complete. Using synchronize_rcu or call_rcu will suffice for this
+ * because both wait for napi context to exit.
  */
 void __dev_flush(void)
 {
 	struct list_head *flush_list = this_cpu_ptr(&dev_flush_list);
 	struct xdp_dev_bulk_queue *bq, *tmp;
 
-	rcu_read_lock();
 	list_for_each_entry_safe(bq, tmp, flush_list, flush_node)
 		bq_xmit_all(bq, XDP_XMIT_FLUSH);
-	rcu_read_unlock();
 }
 
 /* rcu_read_lock (from syscall and BPF contexts) ensures that if a delete and/or
@@ -502,12 +506,11 @@ static int dev_map_delete_elem(struct bpf_map *map, void *key)
 		return -EINVAL;
 
 	/* Use call_rcu() here to ensure any rcu critical sections have
-	 * completed, but this does not guarantee a flush has happened
-	 * yet. Because driver side rcu_read_lock/unlock only protects the
-	 * running XDP program. However, for pending flush operations the
-	 * dev and ctx are stored in another per cpu map. And additionally,
-	 * the driver tear down ensures all soft irqs are complete before
-	 * removing the net device in the case of dev_put equals zero.
+	 * completed as well as any flush operations because call_rcu
+	 * will wait for preempt-disable region to complete, NAPI in this
+	 * context.  And additionally, the driver tear down ensures all
+	 * soft irqs are complete before removing the net device in the
+	 * case of dev_put equals zero.
 	 */
 	old_dev = xchg(&dtab->netdev_map[k], NULL);
 	if (old_dev)