netdev - Re: [PATCH net-next 1/5] ipv6: addrconf: cleanup locking in ipv6_add

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Date:   Sun, 15 Oct 2017 09:24:07 -0600
From:   David Ahern <dsahern@...il.com>
To:     Ido Schimmel <idosch@...sch.org>
Cc:     netdev@...r.kernel.org, jiri@...lanox.com, idosch@...lanox.com,
        kjlx@...pleofstupid.com, davem@...emloft.net,
        yoshfuji@...ux-ipv6.org
Subject: Re: [PATCH net-next 1/5] ipv6: addrconf: cleanup locking in
 ipv6_add_addr

On 10/15/17 1:50 AM, Ido Schimmel wrote:
> On Fri, Oct 13, 2017 at 04:02:09PM -0700, David Ahern wrote:
>> ipv6_add_addr is called in process context with rtnl lock held
>> (e.g., manual config of an address) or during softirq processing
>> (e.g., autoconf and address from a router advertisement).
>>
>> Currently, ipv6_add_addr calls rcu_read_lock_bh shortly after entry
>> and does not call unlock until exit, minus the call around the address
>> validator notifier. Similarly, addrconf_hash_lock is taken after the
>> validator notifier and held until exit. This forces the allocation of
>> inet6_ifaddr to always be atomic.
>>
>> Refactor ipv6_add_addr as follows:
>> 1. add an input boolean to discriminate the call path (process context
>>    or softirq). This new flag controls whether the alloc can be done
>>    with GFP_KERNEL or GFP_ATOMIC.
>>
>> 2. Move the rcu_read_lock_bh and unlock calls only around functions that
>>    do rcu updates.
>>
>> 3. Remove the in6_dev_hold and put added by 3ad7d2468f79f ("Ipvlan should
>>    return an error when an address is already in use."). This was done
>>    presumably because rcu_read_unlock_bh needs to be called before calling
>>    the validator. Since rcu_read_lock is not needed before the validator
>>    runs revert the hold and put added by 3ad7d2468f79f and only do the
>>    hold when setting ifp->idev.
>>
>> 4. move duplicate address check and insertion of new address in the global
>>    address hash into a helper. The helper is called after an ifa is
>>    allocated and filled in.
>>
>> This allows the ifa for manually configured addresses to be done with
>> GFP_KERNEL and reduces the overall amount of time with rcu_read_lock held
>> and hash table spinlock held.
>>
>> Signed-off-by: David Ahern <dsahern@...il.com>
> 
> [...]
> 
>> @@ -1073,21 +1085,19 @@ ipv6_add_addr(struct inet6_dev *idev, const struct in6_addr *addr,
>>  
>>  	in6_ifa_hold(ifa);
>>  	write_unlock(&idev->lock);
>> -out2:
>> +
>>  	rcu_read_unlock_bh();
>>  
>> -	if (likely(err == 0))
>> -		inet6addr_notifier_call_chain(NETDEV_UP, ifa);
>> -	else {
>> +	inet6addr_notifier_call_chain(NETDEV_UP, ifa);
>> +out:
>> +	if (unlikely(err < 0)) {
>> +		if (rt)
>> +			ip6_rt_put(rt);
> 
> I believe 'rt' needs to be set to NULL after addrconf_dst_alloc()
> fails.

The above frees rt and the line below frees the ifa and resets the value
to an error, so after the line above rt is no longer referenced.

Taking a look at this again, I think I am missing an idev put in the
error path here.

> 
>>  		kfree(ifa);
>> -		in6_dev_put(idev);
>>  		ifa = ERR_PTR(err);
>>  	}
>>  
>>  	return ifa;
>> -out:
>> -	spin_unlock(&addrconf_hash_lock);
>> -	goto out2;
>>  }