Re: [PATCH 2/4] net: hsr: shrink seqnr_lock to sequence counter updates

Commit 06afd2c31d33 ("hsr: Synchronize sending frames to have always
incremented outgoing seq nr.") and commit 430d67bdcb04 ("net: hsr: Use
the seqnr lock for frames received via interlink port.") hold
seqnr_lock across the whole forwarding path. Transmitting while
holding the lock can create lock-dependency issues when HSR devices
are stacked with other net devices, up to a real deadlock (see
Reported-by/Closes).

Since commit aae9d6b616b5 ("hsr: Implement more robust duplicate
discard for HSR"), duplicate discard is order-independent (sparse
bitmaps), so only the sequence counter updates need serialization.
Limit seqnr_lock to the counter updates in handle_std_frame(); the
master TX path (hsr_dev_xmit()) and the interlink RX path
(hsr_handle_frame()) drop their outer lock, and the supervision frame
builders release it right after their counter update.

Concurrent forwarding may emit frames out of allocation order, which
sparse-bitmap discard tolerates. The master/interlink tx statistics are
no longer serialized; consistent per-cpu/per-queue statistics for all
HSR paths are handled in a separate series.

Fixes: 06afd2c31d33 ("hsr: Synchronize sending frames to have always incremented outgoing seq nr.")
Fixes: 430d67bdcb04 ("net: hsr: Use the seqnr lock for frames received via interlink port.")
Reported-by: <redacted>
Closes: https://syzkaller.appspot.com/bug?extid=fbf74291c3b7e753b481
Cc: <redacted> # aae9d6b616b5: hsr: Implement more robust duplicate discard for HSR
Signed-off-by: Xin Xie <redacted>
---
 net/hsr/hsr_device.c  | 15 ++++-----------
 net/hsr/hsr_forward.c |  3 ++-
 net/hsr/hsr_slave.c   | 11 +----------
 3 files changed, 7 insertions(+), 22 deletions(-)

diff --git a/net/hsr/hsr_device.c b/net/hsr/hsr_device.c
index 5555b71ab19b..3fd1762d8916 100644
--- a/net/hsr/hsr_device.c
+++ b/net/hsr/hsr_device.c

@@ -232,9 +232,7 @@ static netdev_tx_t hsr_dev_xmit(struct sk_buff *skb, struct net_device *dev)
 		skb->dev = master->dev;
 		skb_reset_mac_header(skb);
 		skb_reset_mac_len(skb);
-		spin_lock_bh(&hsr->seqnr_lock);
 		hsr_forward_skb(skb, master);
-		spin_unlock_bh(&hsr->seqnr_lock);
 	} else {
 		dev_core_stats_tx_dropped_inc(dev);
 		dev_kfree_skb_any(skb);

@@ -335,6 +333,7 @@ static void send_hsr_supervision_frame(struct hsr_port *port,
 		hsr_stag->sequence_nr = htons(hsr->sequence_nr);
 		hsr->sequence_nr++;
 	}
+	spin_unlock_bh(&hsr->seqnr_lock);
 
 	hsr_stag->tlv.HSR_TLV_type = type;
 	/* HSRv0 has 6 unused bytes after the MAC */

@@ -356,14 +355,10 @@ static void send_hsr_supervision_frame(struct hsr_port *port,
 		ether_addr_copy(hsr_sp->macaddress_A, hsr->macaddress_redbox);
 	}
 
-	if (skb_put_padto(skb, ETH_ZLEN)) {
-		spin_unlock_bh(&hsr->seqnr_lock);
+	if (skb_put_padto(skb, ETH_ZLEN))
 		return;
-	}
 
 	hsr_forward_skb(skb, port);
-	spin_unlock_bh(&hsr->seqnr_lock);
-	return;
 }
 
 static void send_prp_supervision_frame(struct hsr_port *master,

@@ -390,6 +385,7 @@ static void send_prp_supervision_frame(struct hsr_port *master,
 	spin_lock_bh(&hsr->seqnr_lock);
 	hsr_stag->sequence_nr = htons(hsr->sup_sequence_nr);
 	hsr->sup_sequence_nr++;
+	spin_unlock_bh(&hsr->seqnr_lock);
 	hsr_stag->tlv.HSR_TLV_type = PRP_TLV_LIFE_CHECK_DD;
 	hsr_stag->tlv.HSR_TLV_length = sizeof(struct hsr_sup_payload);
 

@@ -397,13 +393,10 @@ static void send_prp_supervision_frame(struct hsr_port *master,
 	hsr_sp = skb_put(skb, sizeof(struct hsr_sup_payload));
 	ether_addr_copy(hsr_sp->macaddress_A, master->dev->dev_addr);
 
-	if (skb_put_padto(skb, ETH_ZLEN)) {
-		spin_unlock_bh(&hsr->seqnr_lock);
+	if (skb_put_padto(skb, ETH_ZLEN))
 		return;
-	}
 
 	hsr_forward_skb(skb, master);
-	spin_unlock_bh(&hsr->seqnr_lock);
 }
 
 /* Announce (supervision frame) timer function

diff --git a/net/hsr/hsr_forward.c b/net/hsr/hsr_forward.c
index 0774981a65c1..8e4158a9b57c 100644
--- a/net/hsr/hsr_forward.c
+++ b/net/hsr/hsr_forward.c

@@ -621,9 +621,10 @@ static void handle_std_frame(struct sk_buff *skb,
 	if (port->type == HSR_PT_MASTER ||
 	    port->type == HSR_PT_INTERLINK) {
 		/* Sequence nr for the master/interlink node */
-		lockdep_assert_held(&hsr->seqnr_lock);
+		spin_lock_bh(&hsr->seqnr_lock);
 		frame->sequence_nr = hsr->sequence_nr;
 		hsr->sequence_nr++;
+		spin_unlock_bh(&hsr->seqnr_lock);
 	}
 }
 

diff --git a/net/hsr/hsr_slave.c b/net/hsr/hsr_slave.c
index bb2182a169a3..8b96eafe15b3 100644
--- a/net/hsr/hsr_slave.c
+++ b/net/hsr/hsr_slave.c

@@ -73,16 +73,7 @@ static rx_handler_result_t hsr_handle_frame(struct sk_buff **pskb)
 	}
 	skb_reset_mac_len(skb);
 
-	/* Only the frames received over the interlink port will assign a
-	 * sequence number and require synchronisation vs other sender.
-	 */
-	if (port->type == HSR_PT_INTERLINK) {
-		spin_lock_bh(&hsr->seqnr_lock);
-		hsr_forward_skb(skb, port);
-		spin_unlock_bh(&hsr->seqnr_lock);
-	} else {
-		hsr_forward_skb(skb, port);
-	}
+	hsr_forward_skb(skb, port);
 
 finish_consume:
 	return RX_HANDLER_CONSUMED;

-- 
2.43.0