Re: [PATCH][XFRM] Replace rwlock on xfrm_policy_afinfo with rcu
From: Eric Dumazet <hidden>
Date: 2012-08-08 06:25:51
On Tue, 2012-08-07 at 10:51 +0530, Priyanka Jain wrote:
xfrm_policy_afinfo is read mosly data structure. Write on xfrm_policy_afinfo is done only at the time of configuration. So rwlocks can be safely replaced with RCU. RCUs usage optimizes the performance.
quoted hunk ↗ jump to hunk
static struct xfrm_policy_afinfo *xfrm_policy_get_afinfo(unsigned short family)@@ -2530,16 +2535,16 @@ static struct xfrm_policy_afinfo *xfrm_policy_get_afinfo(unsigned short family) struct xfrm_policy_afinfo *afinfo; if (unlikely(family >= NPROTO)) return NULL; - read_lock(&xfrm_policy_afinfo_lock); - afinfo = xfrm_policy_afinfo[family]; + rcu_read_lock(); + afinfo = rcu_dereference(xfrm_policy_afinfo[family]); if (unlikely(!afinfo)) - read_unlock(&xfrm_policy_afinfo_lock); + rcu_read_unlock();
This makes no sense to me : We cant safely return afinfo here. Note the current code is buggy as well, this is worrying. As soon as we exit from xfrm_policy_get_afinfo(), pointer might be invalid. Really, RCU conversion should be the right moment to spot those bugs and first fix them (for stable trees)