Subject: Re: [PATCHv2 ipsec-next] xfrm: Namespacify xfrm_policy_sk_bundles

From: Fan Du <[email-masked]>
Date: Wed, 18 Dec 2013 13:33:58 +0800

On 2013年12月18日 12:50, Eric Dumazet wrote:
> On Wed, 2013-12-18 at 11:34 +0800, Fan Du wrote:
>> xfrm_policy_sk_bundles, protected by net->xfrm.xfrm_policy_sk_bundle_lock
>> should be put into netns xfrm structure, otherwise xfrm_policy_sk_bundles
>> can be corrupted from different net namespace.
>>
>> Moreover current xfrm_policy_sk_bundle_lock used in below two scenarios:
>>
>> 1. xfrm_lookup(Process context)  vs  __xfrm_garbage_collect(softirq context)
>> 2. xfrm_lookup(Process context)  vs  __xfrm_garbage_collect(Process context
>>                                                  when SPD change or dev down)
>>
>> we can use xchg to avoid the spinlock, at the same time cover above scenarios,
>> inspired by discussion in: http://marc.info/?l=linux-netdev&m=138713363113003&w=2
>>
>> Signed-off-by: Fan Du<[email-masked]>
>> ---
>> v2:
>>    Fix incorrect commit log.
>>
>> ---
>>   include/net/netns/xfrm.h |    2 +-
>>   net/xfrm/xfrm_policy.c   |   17 +++--------------
>>   2 files changed, 4 insertions(+), 15 deletions(-)
>>
>> diff --git a/include/net/netns/xfrm.h b/include/net/netns/xfrm.h
>> index 1006a26..4a30b1b 100644
>> --- a/include/net/netns/xfrm.h
>> +++ b/include/net/netns/xfrm.h
>> @@ -58,9 +58,9 @@ struct netns_xfrm {
>>   	struct dst_ops		xfrm6_dst_ops;
>>   #endif
>>   	spinlock_t xfrm_state_lock;
>> -	spinlock_t xfrm_policy_sk_bundle_lock;
>>   	rwlock_t xfrm_policy_lock;
>>   	struct mutex xfrm_cfg_mutex;
>> +	struct dst_entry *xfrm_policy_sk_bundles;
>>   };
>>
>>   #endif
>> diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c
>> index a7487f3..26d79c0 100644
>> --- a/net/xfrm/xfrm_policy.c
>> +++ b/net/xfrm/xfrm_policy.c
>> @@ -39,8 +39,6 @@
>>   #define XFRM_QUEUE_TMO_MAX ((unsigned)(60*HZ))
>>   #define XFRM_MAX_QUEUE_LEN	100
>>
>> -static struct dst_entry *xfrm_policy_sk_bundles;
>> -
>>   static DEFINE_SPINLOCK(xfrm_policy_afinfo_lock);
>>   static struct xfrm_policy_afinfo __rcu *xfrm_policy_afinfo[NPROTO]
>>   						__read_mostly;
>> @@ -2108,12 +2106,8 @@ struct dst_entry *xfrm_lookup(struct net *net, struct dst_entry *dst_orig,
>>   			}
>>
>>   			dst_hold(&xdst->u.dst);
>> -
>> -			spin_lock_bh(&net->xfrm.xfrm_policy_sk_bundle_lock);
>> -			xdst->u.dst.next = xfrm_policy_sk_bundles;
>> -			xfrm_policy_sk_bundles =&xdst->u.dst;
>> -			spin_unlock_bh(&net->xfrm.xfrm_policy_sk_bundle_lock);
>> -
>> +			xdst->u.dst.next = xchg(&net->xfrm.xfrm_policy_sk_bundles,
>> +						&xdst->u.dst);
>
> This is not safe.
>
> Take a look at include/linux/llist.h if you really want to avoid the
> spinlock.

Hi Eric

Thanks for your attention,
I'm not follow why xchg here is unsafe, could you please elaborate a bit more?

-- 
浮沉随浪只记今朝笑

--fan