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

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Message-ID: <8760avxtx5.fsf@vitty.brq.redhat.com>
Date:   Tue, 31 Oct 2017 15:40:06 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        devel@...uxdriverproject.org,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>
Subject: Re: [PATCH net-next 3/4] hv_netvsc: reset net_device_ctx->nvdev with rcu_assign_pointer()

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.

-- 
  Vitaly