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

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Message-Id: <20171031.234459.546020444648753386.davem@davemloft.net>
Date:   Tue, 31 Oct 2017 23:44:59 +0900 (KST)
From:   David Miller <davem@...emloft.net>
To:     vkuznets@...hat.com
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()

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.

Thank you.