On Fri, Nov 21, 2014 at 7:05 PM, Eric Dumazet <eric.dumazet@xxxxxxxxx> wrote: > > On Fri, 2014-11-21 at 16:57 -0500, Pranith Kumar wrote: > >> Hi Eric, >> >> Thanks for looking at this patch. >> >> I've been scratching my head since morning trying to find out what was >> so obviously wrong with this patch. Alas, I don't see what you do. >> >> Could you point it out and show me how incompetent I am, please? >> >> Thanks! > > Well, even it the code is _not_ broken, I don't see any value with this > patch. Phew. Not being broken itself is a win :) > > If I use git blame on current code, line containing > smp_read_barrier_depends() exactly points to the relevant commit [1] And that is an opinion I will respect. I don't want to muck the git history where it is significant. This effort is to eventually replace the uses of smp_read_barrier_depends() and to use either rcu or lockless_dereference() as documented in memory-barriers.txt. > > After your change, it will point to some cleanup, which makes little > sense to me, considering you did not change the smp_wmb() in > xt_replace_table(). That does not need to change as it is fine as it is. It still pairs with the smp_read_barrier_depends() in lockless_dereference(). > > I, as a netfilter contributor would like to keep current code as is, > because it is how I feel safe with it. > > We have a proliferation of interfaces, but this does not help to > understand the issues and code maintenance. > > smp_read_barrier_depends() better documents the read barrier than > lockless_dereference(). I think this is a matter of opinion. But in the current effort I've seen cases where it is not clear what the barrier is actually guaranteeing. I am glad that the current code is not one of those and it has reasonable comments. lockless_dereference() on the other hand makes the dependency explicit. > > The point of having a lock or not is irrelevant here. > > [1] > http://git.kernel.org/cgit/linux/kernel/git/davem/net.git/commit/?id=b416c144f46af1a30ddfa4e4319a8f077381ad63 > > > > Thanks! -- Pranith -- 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
