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Subject: Re: [PATCH net] net: nixge: fix potential memory leak in
 nixge_start_xmit()
To:     Saeed Mahameed <saeed@kernel.org>
CC:     Francois Romieu <romieu@fr.zoreil.com>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        Moritz Fischer <mdf@kernel.org>, <netdev@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>
References: <1668416136-33530-1-git-send-email-zhangchangzhong@huawei.com>
 <Y3IbBCioK1Clt/3a@electric-eye.fr.zoreil.com>
 <21641ba0-3ce1-c409-b513-1bbbaeccaa51@huawei.com> <Y3Vl40BzsL9nFqQv@x130.lan>
From:   Zhang Changzhong <zhangchangzhong@huawei.com>
Message-ID: <a84e51e3-3f19-51f3-e4f5-12cfa13aa548@huawei.com>
Date:   Thu, 17 Nov 2022 11:04:23 +0800
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On 2022/11/17 6:36, Saeed Mahameed wrote:
> On 15 Nov 21:20, Zhang Changzhong wrote:
>> On 2022/11/14 18:40, Francois Romieu wrote:
>>> Zhang Changzhong <zhangchangzhong@huawei.com> :
>>>> The nixge_start_xmit() returns NETDEV_TX_OK but does not free skb on two
>>>> error handling cases, which can lead to memory leak.
>>>>
>>>> To fix this, return NETDEV_TX_BUSY in case of nixge_check_tx_bd_space()
>>>> fails and add dev_kfree_skb_any() in case of dma_map_single() fails.
>>>
>>> This patch merge two unrelated changes. Please split.
>>>
>>>> Fixes: 492caffa8a1a ("net: ethernet: nixge: Add support for National Instruments XGE netdev")
>>>> Signed-off-by: Zhang Changzhong <zhangchangzhong@huawei.com>
>>>> ---
>>>>  drivers/net/ethernet/ni/nixge.c | 6 ++++--
>>>>  1 file changed, 4 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/drivers/net/ethernet/ni/nixge.c b/drivers/net/ethernet/ni/nixge.c
>>>> index 19d043b593cc..b9091f9bbc77 100644
>>>> --- a/drivers/net/ethernet/ni/nixge.c
>>>> +++ b/drivers/net/ethernet/ni/nixge.c
>>>> @@ -521,13 +521,15 @@ static netdev_tx_t nixge_start_xmit(struct sk_buff *skb,
>>>>      if (nixge_check_tx_bd_space(priv, num_frag)) {
>>>>          if (!netif_queue_stopped(ndev))
>>>>              netif_stop_queue(ndev);
>>>> -        return NETDEV_TX_OK;
>>>> +        return NETDEV_TX_BUSY;
>>>>      }
>>>
>>> The driver should probably check the available room before returning
>>> from hard_start_xmit and turn the check above unlikely().
>>>
>>> Btw there is no lock and the Tx completion is irq driven: the driver
>>> is racy. :o(
>>>
>>
>> Hi Francois,
>>
>> Thanks for you review. I'll make v2 according to your suggestion.
>>
> 
> you will probably need to check out: Transmit path guidelines:
> https://www.kernel.org/doc/Documentation/networking/driver.rst
> 

Thank! This document is very helpful.

> .