netdev - Re: [PATCH net-next 01/10] netdevsim: fib: Convert the current occupancy to an atomic variable

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Date:   Wed, 27 Jan 2021 20:42:17 -0700
From:   David Ahern <dsahern@...il.com>
To:     Amit Cohen <amcohen@...dia.com>, Ido Schimmel <idosch@...sch.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Cc:     "davem@...emloft.net" <davem@...emloft.net>,
        "kuba@...nel.org" <kuba@...nel.org>,
        Roopa Prabhu <roopa@...dia.com>,
        Donald Sharp <sharpd@...dia.com>,
        Benjamin Poirier <bpoirier@...dia.com>,
        mlxsw <mlxsw@...dia.com>, Ido Schimmel <idosch@...dia.com>
Subject: Re: [PATCH net-next 01/10] netdevsim: fib: Convert the current
 occupancy to an atomic variable

On 1/27/21 3:51 AM, Amit Cohen wrote:
> 
> 
>> -----Original Message-----
>> From: David Ahern <dsahern@...il.com>
>> Sent: Wednesday, January 27, 2021 6:33
>> To: Ido Schimmel <idosch@...sch.org>; netdev@...r.kernel.org
>> Cc: davem@...emloft.net; kuba@...nel.org; Amit Cohen <amcohen@...dia.com>; Roopa Prabhu <roopa@...dia.com>; Donald
>> Sharp <sharpd@...dia.com>; Benjamin Poirier <bpoirier@...dia.com>; mlxsw <mlxsw@...dia.com>; Ido Schimmel
>> <idosch@...dia.com>
>> Subject: Re: [PATCH net-next 01/10] netdevsim: fib: Convert the current occupancy to an atomic variable
>>
>> On 1/26/21 6:23 AM, Ido Schimmel wrote:
>>> @@ -889,22 +882,29 @@ static void nsim_nexthop_destroy(struct
>>> nsim_nexthop *nexthop)  static int nsim_nexthop_account(struct nsim_fib_data *data, u64 occ,
>>>  				bool add, struct netlink_ext_ack *extack)  {
>>> -	int err = 0;
>>> +	int i, err = 0;
>>>
>>>  	if (add) {
>>> -		if (data->nexthops.num + occ <= data->nexthops.max) {
>>> -			data->nexthops.num += occ;
>>> -		} else {
>>> -			err = -ENOSPC;
>>> -			NL_SET_ERR_MSG_MOD(extack, "Exceeded number of supported nexthops");
>>> -		}
>>> +		for (i = 0; i < occ; i++)
>>> +			if (!atomic64_add_unless(&data->nexthops.num, 1,
>>> +						 data->nexthops.max)) {
>>
>> seems like this can be
>> 		if (!atomic64_add_unless(&data->nexthops.num, occ,
>> 					 data->nexthops.max)) {
> 
> atomic64_add_unless(x, y, z) adds y to x if x was not already z.
> Which means that when for example num=2, occ=2, max=3:
> atomic64_add_unless(&data->nexthops.num, occ, data->nexthops.max) won't fail when it should.
> 

ok, missed that in the description. I thought it was if the total would
equal or be greater than z.