Question on rcu_access_pointer, rcu_assign_pointer and locking.

Hello!

I'm trying to better understand some code in net/mac80211/scan.c in order to track down some memory leaks reported by kmemleak.

My question boils down to this. Assume we have code similar to this:

spin_lock_bh(&dev->bss_lock);
old = rcu_access_pointer(found->pub.beacon_ies); rcu_assign_pointer(found->pub.beacon_ies, tmp->pub.beacon_ies); if (old)

	kfree_rcu((struct cfg80211_bss_ies *)old, rcu_head);

spin_unlock_bh(&dev->bss_lock);

Would it be possible to somehow leak what is assigned to found->pub.beacon_ies, perhaps because two threads managed to go through this
code within a single RCU period?

I think that if the rcu_assign_pointer logic wasn't 'published' before a second thread came through this logic it could cause this leakage?

The actual code I'm curious about is in net/mac80211/scan.c, in the cfg80211_bss_update method.

Thanks,
Ben

Ben Greear <[email protected]>
Candela Technologies Inc  http://www.candelatech.com