On Thu, Sep 03, 2009 at 05:44:54PM -0500, Christoph Lameter wrote: > On Thu, 3 Sep 2009, Eric Dumazet wrote: > > > It seems very smart, but needs review of all callers to make sure no slabs > > are waiting for final freeing in call_rcu queue on some cpu. > > Yes. Again this is the first time we encounter a situation where a > DESTROY_BY_RCU slab has to be destroyed. So the review is quite short. > > > I suspect most of them will then have to use rcu_barrier() before calling > > kmem_cache_destroy(), so why not factorizing code in one place ? > > There are different forms of RCU which require different forms of > barriers. Its best to leave that up to the user. Again the user must make > sure that no objects are in use before a slab is destroyed. For > SLAB_DESTROY_BY_RCU this means that there are no potential outstanding > reads on the structure. You may need an rcu_barrier() to accomplish that. > > Slight variations in the use of RCU could require different method. Better > reduce the entanglement of slabs to RCU to a mininum possible. If it were the user of the slab who was invoking some variant of call_rcu(), then I would agree with you. However, call_rcu() is instead being invoked by the slab itself in the case of SLAB_DESTROY_BY_RCU, so that there is no variation in usage. Requiring that the user call rcu_barrier() is asking for subtle bugs. Therefore, the best approach is to have kmem_cache_destroy() handle the RCU cleanup, given that this cleanup is for actions taken by kmem_cache_free(), not by the user. Thanx, Paul -- To unsubscribe from this list: send the line "unsubscribe netfilter-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
