linux-kernel - Re: [PATCH net-next 3/4] hv_netvsc: reset net_device_ctx->nvdev with rcu_assign

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Message-ID: <871sljxtfa.fsf@vitty.brq.redhat.com>
Date:   Tue, 31 Oct 2017 15:50:49 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     David Miller <davem@...emloft.net>
Cc:     eric.dumazet@...il.com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, devel@...uxdriverproject.org,
        kys@...rosoft.com, haiyangz@...rosoft.com, sthemmin@...rosoft.com
Subject: Re: [PATCH net-next 3/4] hv_netvsc: reset net_device_ctx->nvdev with rcu_assign_pointer()

David Miller <davem@...emloft.net> writes:

> From: Vitaly Kuznetsov <vkuznets@...hat.com>
> Date: Tue, 31 Oct 2017 15:40:06 +0100
>
>> Eric Dumazet <eric.dumazet@...il.com> writes:
>> 
>>> On Tue, 2017-10-31 at 14:42 +0100, Vitaly Kuznetsov wrote:
>>>> RCU_INIT_POINTER() is not suitable here as it doesn't give us ordering
>>>> guarantees (see the comment in rcupdate.h). This is also not a hotpath.
>>>> 
>>>> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
>>>> ---
>>>>  drivers/net/hyperv/netvsc.c | 2 +-
>>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>> 
>>>> diff --git a/drivers/net/hyperv/netvsc.c b/drivers/net/hyperv/netvsc.c
>>>> index bfc79698b8f4..12efb3e34775 100644
>>>> --- a/drivers/net/hyperv/netvsc.c
>>>> +++ b/drivers/net/hyperv/netvsc.c
>>>> @@ -560,7 +560,7 @@ void netvsc_device_remove(struct hv_device *device)
>>>>  
>>>>  	netvsc_revoke_buf(device, net_device);
>>>>  
>>>> -	RCU_INIT_POINTER(net_device_ctx->nvdev, NULL);
>>>> +	rcu_assign_pointer(net_device_ctx->nvdev, NULL);
>>>
>>> I see no point for this patch.
>>>
>>> Setting a NULL pointer needs no barrier at all.
>> 
>> Oh, sorry, I got confused by the comment near RCU_INIT_POINTER() in
>> rcupdate.h. Now looking at their definitions I see.
>> 
>> This patch can of course be dropped from the series.
>
> Any time there is a change to the series, you must resubmit the entire
> series.
>

Sure, will do. Just wanted to give it a couple of days to see if
Microsoft guys or someone else have any comments.

Thanks,

-- 
  Vitaly