Re: [PATCH 3/3] Convert the UDP hash lock to RCU

[Eric Dumazet]

Peter Zijlstra a écrit :
> On Mon, 2008-10-06 at 23:22 +0200, Eric Dumazet wrote:
>
> > Or just add SLAB_DESTROY_BY_RCU to slab creation in proto_register()
> > for "struct proto udp_prot/udpv6_prot" so that kmem_cache_free() 
> > done in sk_prot_free() can defer freeing to RCU...
>
> Be careful!, SLAB_DESTROY_BY_RCU just means the slab page gets
> RCU-freed, this means that slab object pointers stay pointing to valid
> memory, but it does _NOT_ mean those slab objects themselves remain
> valid.
>
> The slab allocator is free to re-use those objects at any time -
> irrespective of the rcu-grace period. Therefore you will have to be able
> to validate that the object you point to is indeed the object you
> expect, otherwise strange and wonderful things will happen.
Thanks for this clarification. I guess we really need a rcu head then :)



--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/