[PATCH net] net: hns: fix soft lockup when there is not enough memory

[PATCH net] net: hns: fix soft lockup when there is not enough memory

[Yonglong Liu]

When there is not enough memory and napi_alloc_skb() return NULL,
the HNS driver will print error message, and than try again, if
the memory is not enough for a while, huge error message and the
retry operation will cause soft lockup.

When napi_alloc_skb() return NULL because of no memory, we can
get a warn_alloc() call trace, so this patch deletes the error
message. We already use polling mode to handle irq, but the
retry operation will render the polling weight inactive, this
patch just return budget when the rx is not completed to avoid
dead loop.

Fixes: 36eedfde1a36 ("net: hns: Optimize hns_nic_common_poll for better performance")
Fixes: b5996f11ea54 ("net: add Hisilicon Network Subsystem basic ethernet support")
Signed-off-by: Yonglong Liu <liuyonglong@huawei.com>
---
 drivers/net/ethernet/hisilicon/hns/hns_enet.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/drivers/net/ethernet/hisilicon/hns/hns_enet.c b/drivers/net/ethernet/hisilicon/hns/hns_enet.c
index 14ab204..eb69e5c 100644
--- a/drivers/net/ethernet/hisilicon/hns/hns_enet.c
+++ b/drivers/net/ethernet/hisilicon/hns/hns_enet.c
@@ -565,7 +565,6 @@ static int hns_nic_poll_rx_skb(struct hns_nic_ring_data *ring_data,
 	skb = *out_skb = napi_alloc_skb(&ring_data->napi,
 					HNS_RX_HEAD_SIZE);
 	if (unlikely(!skb)) {
-		netdev_err(ndev, "alloc rx skb fail\n");
 		ring->stats.sw_err_cnt++;
 		return -ENOMEM;
 	}
@@ -1056,7 +1055,6 @@ static int hns_nic_common_poll(struct napi_struct *napi, int budget)
 		container_of(napi, struct hns_nic_ring_data, napi);
 	struct hnae_ring *ring = ring_data->ring;
 
-try_again:
 	clean_complete += ring_data->poll_one(
 				ring_data, budget - clean_complete,
 				ring_data->ex_process);
@@ -1066,7 +1064,7 @@ static int hns_nic_common_poll(struct napi_struct *napi, int budget)
 			napi_complete(napi);
 			ring->q->handle->dev->ops->toggle_ring_irq(ring, 0);
 		} else {
-			goto try_again;
+			return budget;
 		}
 	}
 
-- 
2.8.1

Re: [PATCH net] net: hns: fix soft lockup when there is not enough memory

[David Miller]

From: Yonglong Liu <liuyonglong@huawei.com>
Date: Thu, 16 Jan 2020 15:41:17 +0800

> When there is not enough memory and napi_alloc_skb() return NULL,
> the HNS driver will print error message, and than try again, if
> the memory is not enough for a while, huge error message and the
> retry operation will cause soft lockup.
> 
> When napi_alloc_skb() return NULL because of no memory, we can
> get a warn_alloc() call trace, so this patch deletes the error
> message. We already use polling mode to handle irq, but the
> retry operation will render the polling weight inactive, this
> patch just return budget when the rx is not completed to avoid
> dead loop.
> 
> Fixes: 36eedfde1a36 ("net: hns: Optimize hns_nic_common_poll for better performance")
> Fixes: b5996f11ea54 ("net: add Hisilicon Network Subsystem basic ethernet support")
> Signed-off-by: Yonglong Liu <liuyonglong@huawei.com>

Applied and queued up for -stable.