[dpdk-dev] 答复: [PATCH] net/bonding: fix double fetch for active_slave_count
Chas Williams
3chas3 at gmail.com
Fri Nov 30 23:28:09 CET 2018
The problem is that I can't see how the API can ever provide accurate
information. By the time you have the information it is potentially
stale. There really isn't a way to control if a slave is active since
that is protocol dependent.
rte_eth_bond_slaves_get() is safer in the sense that you control when
the slaves are added and removed from the bonding group. You can ensure
that you get a consistent answer.
Hopefully your protocol doesn't especially care if the slave is active
or not. You are sending the packets via rte_eth_bond_8023ad_ext_slow()?
On 11/30/18 12:50 AM, Linhaifeng wrote:
> Hi, Chars
>
> Thank you.
>
> I use it for send pkts to the dedicated queue of slaves.
>
> Maybe i should not use it. I would though another way.
>
> -----邮件原件-----
> 发件人: Chas Williams [mailto:3chas3 at gmail.com]
> 发送时间: 2018年11月30日 11:27
> 收件人: Linhaifeng <haifeng.lin at huawei.com>; dev at dpdk.org
> 抄送: chas3 at att.com
> 主题: Re: [dpdk-dev] [PATCH] net/bonding: fix double fetch for active_slave_count
>
> I guess this is slightly more correct. There is still a race here though.
> After you make your copy of active_slave_count, the number of active slaves could go to 0 and the memcpy() would copy an invalid element, acitve_slaves[0]. There is no simple fix to this problem. Your patch reduces the opportunity for a race but doesn't eliminate it.
>
> What you are using this API for?
>
> On 11/29/18 12:32 AM, Haifeng Lin wrote:
>> 1. when memcpy slaves the internals->active_slave_count 1 2. return
>> internals->active_slave_count is 2 3. the slaves[1] would be a random
>> invalid value
>>
>> Signed-off-by: Haifeng Lin <haifeng.lin at huawei.com>
>> ---
>> drivers/net/bonding/rte_eth_bond_api.c | 8 +++++---
>> 1 file changed, 5 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/net/bonding/rte_eth_bond_api.c
>> b/drivers/net/bonding/rte_eth_bond_api.c
>> index 21bcd50..ed7b02e 100644
>> --- a/drivers/net/bonding/rte_eth_bond_api.c
>> +++ b/drivers/net/bonding/rte_eth_bond_api.c
>> @@ -815,6 +815,7 @@
>> uint16_t len)
>> {
>> struct bond_dev_private *internals;
>> + uint16_t active_slave_count;
>>
>> if (valid_bonded_port_id(bonded_port_id) != 0)
>> return -1;
>> @@ -824,13 +825,14 @@
>>
>> internals = rte_eth_devices[bonded_port_id].data->dev_private;
>>
>> - if (internals->active_slave_count > len)
>> + active_slave_count = internals->active_slave_count;
>> + if (active_slave_count > len)
>> return -1;
>>
>> memcpy(slaves, internals->active_slaves,
>> - internals->active_slave_count * sizeof(internals->active_slaves[0]));
>> + active_slave_count * sizeof(internals->active_slaves[0]));
>>
>> - return internals->active_slave_count;
>> + return active_slave_count;
>> }
>>
>> int
>>
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