[PATCH] af_packet: TPACKET_V3: fix fill status rwlock imbalance

[John Ogness]

After @blk_fill_in_prog_lock is acquired there is an early out vnet
situation that can occur. In that case, the rwlock needs to be
released.

Also, since @blk_fill_in_prog_lock is only acquired when @tp_version
is exactly TPACKET_V3, only release it on that exact condition as
well.

And finally, add sparse annotation so that it is clearer that
prb_fill_curr_block() and prb_clear_blk_fill_status() are acquiring
and releasing @blk_fill_in_prog_lock, respectively. sparse is still
unable to understand the balance, but the warnings are now on a
higher level that make more sense.

Fixes: 632ca50f2cbd ("af_packet: TPACKET_V3: replace busy-wait loop")
Signed-off-by: John Ogness <john.ogness@xxxxxxxxxxxxx>
Reported-by: kernel test robot <lkp@xxxxxxxxx>
---
 net/packet/af_packet.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 0b8160d1a6e0..479c257ded73 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -941,6 +941,7 @@ static int prb_queue_frozen(struct tpacket_kbdq_core *pkc)
 }
 
 static void prb_clear_blk_fill_status(struct packet_ring_buffer *rb)
+	__releases(&pkc->blk_fill_in_prog_lock)
 {
 	struct tpacket_kbdq_core *pkc  = GET_PBDQC_FROM_RB(rb);
 
@@ -989,6 +990,7 @@ static void prb_fill_curr_block(char *curr,
 				struct tpacket_kbdq_core *pkc,
 				struct tpacket_block_desc *pbd,
 				unsigned int len)
+	__acquires(&pkc->blk_fill_in_prog_lock)
 {
 	struct tpacket3_hdr *ppd;
 
@@ -2286,8 +2288,11 @@ static int tpacket_rcv(struct sk_buff *skb, struct net_device *dev,
 	if (do_vnet &&
 	    virtio_net_hdr_from_skb(skb, h.raw + macoff -
 				    sizeof(struct virtio_net_hdr),
-				    vio_le(), true, 0))
+				    vio_le(), true, 0)) {
+		if (po->tp_version == TPACKET_V3)
+			prb_clear_blk_fill_status(&po->rx_ring);
 		goto drop_n_account;
+	}
 
 	if (po->tp_version <= TPACKET_V2) {
 		packet_increment_rx_head(po, &po->rx_ring);
@@ -2393,7 +2398,7 @@ static int tpacket_rcv(struct sk_buff *skb, struct net_device *dev,
 		__clear_bit(slot_id, po->rx_ring.rx_owner_map);
 		spin_unlock(&sk->sk_receive_queue.lock);
 		sk->sk_data_ready(sk);
-	} else {
+	} else if (po->tp_version == TPACKET_V3) {
 		prb_clear_blk_fill_status(&po->rx_ring);
 	}
 
-- 
2.20.1