[PATCH net] net: hns: Fix the stray netpoll locks causing deadlock in NAPI path

* [PATCH net] net: hns: Fix the stray netpoll locks causing deadlock in NAPI path
@ 2019-11-06 18:54 Salil Mehta
  2019-11-07 14:12 ` Marc Zyngier
  0 siblings, 1 reply; 3+ messages in thread
From: Salil Mehta @ 2019-11-06 18:54 UTC (permalink / raw)
  To: davem, maz
  Cc: edumazet, salil.mehta, yisen.zhuang, lipeng321, mehta.salil,
	netdev, linux-kernel, linuxarm

This patch fixes the problem of the spin locks, originally
meant for the netpoll path of hns driver, causing deadlock in
the normal NAPI poll path. The issue happened due presence of
the stray leftover spin lock code related to the netpoll,
whose support was earlier removed from the HNS[1], got activated
due to enabling of NET_POLL_CONTROLLER switch.

Earlier background:
The netpoll handling code originally had this bug(as identified
by Marc Zyngier[2]) of wrong spin lock API being used which did
not disable the interrupts and hence could cause locking issues.
i.e. if the lock were first acquired in context to thread like
'ip' util and this lock if ever got later acquired again in
context to the interrupt context like TX/RX (Interrupts could
always pre-empt the lock holding task and acquire the lock again)
and hence could cause deadlock.

Proposed Solution:
1. If the netpoll was enabled in the HNS driver, which is not
   right now, we could have simply used spin_[un]lock_irqsave()
2. But as netpoll is disabled, therefore, it is best to get rid
   of the existing locks and stray code for now. This should
   solve the problem reported by Marc.

@Marc,
Could you please test this patch and confirm if the problem is
fixed at your end?

Many Thanks

[1] https://git.kernel.org/torvalds/c/4bd2c03be7
[2] https://patchwork.ozlabs.org/patch/1189139/

Fixes: 4bd2c03be707 ("net: hns: remove ndo_poll_controller")
Cc: lipeng <lipeng321@huawei.com>
Cc: Yisen Zhuang <yisen.zhuang@huawei.com>
Cc: Eric Dumazet <edumazet@google.com>
Cc: David S. Miller <davem@davemloft.net>
Reported-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Salil Mehta <salil.mehta@huawei.com>
---
 drivers/net/ethernet/hisilicon/hns/hns_enet.c | 22 +------------------
 1 file changed, 1 insertion(+), 21 deletions(-)

diff --git a/drivers/net/ethernet/hisilicon/hns/hns_enet.c b/drivers/net/ethernet/hisilicon/hns/hns_enet.c
index a48396dd4ebb..14ab20491fd0 100644
--- a/drivers/net/ethernet/hisilicon/hns/hns_enet.c
+++ b/drivers/net/ethernet/hisilicon/hns/hns_enet.c
@@ -943,15 +943,6 @@ static int is_valid_clean_head(struct hnae_ring *ring, int h)
 	return u > c ? (h > c && h <= u) : (h > c || h <= u);
 }
 
-/* netif_tx_lock will turn down the performance, set only when necessary */
-#ifdef CONFIG_NET_POLL_CONTROLLER
-#define NETIF_TX_LOCK(ring) spin_lock(&(ring)->lock)
-#define NETIF_TX_UNLOCK(ring) spin_unlock(&(ring)->lock)
-#else
-#define NETIF_TX_LOCK(ring)
-#define NETIF_TX_UNLOCK(ring)
-#endif
-
 /* reclaim all desc in one budget
  * return error or number of desc left
  */
@@ -965,21 +956,16 @@ static int hns_nic_tx_poll_one(struct hns_nic_ring_data *ring_data,
 	int head;
 	int bytes, pkts;
 
-	NETIF_TX_LOCK(ring);
-
 	head = readl_relaxed(ring->io_base + RCB_REG_HEAD);
 	rmb(); /* make sure head is ready before touch any data */
 
-	if (is_ring_empty(ring) || head == ring->next_to_clean) {
-		NETIF_TX_UNLOCK(ring);
+	if (is_ring_empty(ring) || head == ring->next_to_clean)
 		return 0; /* no data to poll */
-	}
 
 	if (!is_valid_clean_head(ring, head)) {
 		netdev_err(ndev, "wrong head (%d, %d-%d)\n", head,
 			   ring->next_to_use, ring->next_to_clean);
 		ring->stats.io_err_cnt++;
-		NETIF_TX_UNLOCK(ring);
 		return -EIO;
 	}
 
@@ -994,8 +980,6 @@ static int hns_nic_tx_poll_one(struct hns_nic_ring_data *ring_data,
 	ring->stats.tx_pkts += pkts;
 	ring->stats.tx_bytes += bytes;
 
-	NETIF_TX_UNLOCK(ring);
-
 	dev_queue = netdev_get_tx_queue(ndev, ring_data->queue_index);
 	netdev_tx_completed_queue(dev_queue, pkts, bytes);
 
@@ -1055,16 +1039,12 @@ static void hns_nic_tx_clr_all_bufs(struct hns_nic_ring_data *ring_data)
 	int head;
 	int bytes, pkts;
 
-	NETIF_TX_LOCK(ring);
-
 	head = ring->next_to_use; /* ntu :soft setted ring position*/
 	bytes = 0;
 	pkts = 0;
 	while (head != ring->next_to_clean)
 		hns_nic_reclaim_one_desc(ring, &bytes, &pkts);
 
-	NETIF_TX_UNLOCK(ring);
-
 	dev_queue = netdev_get_tx_queue(ndev, ring_data->queue_index);
 	netdev_tx_reset_queue(dev_queue);
 }
-- 
2.17.1



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