Re: [PATCH] netfilter: use per-cpu recursive lock (v11)

Eric Dumazet
2009-04-22T16:59:17Z

Linus Torvalds a écrit :
>
> On Wed, 22 Apr 2009, Eric Dumazet wrote:
>> If this could be done without recursion, I am pretty sure netfilter
>> and network guys would have done it. I found Linus reaction quite
>> shocking IMHO, considering hard work done by all people on this.
>
> You don't _understand_ do you?
>
> There is a huge difference between recursive code, and a recursive lock.
>
> The netfilter code may need to occasionally re-enter itself. Nobody ever
> contested _that_ part.
>
> What I have disagreed with the whole time is
>
> (a) doing local ad-hoc locking primitives without any comments
> what-so-ever.
>
> (b) Doing them _wrong_ in many cases
>
> (c) Calling the _lock_ a "recursive" lock.
>
> The fact that a lock works with recursion doesn't make it "recursive".
> That generally has a very special meaning for locking primitives, and
> means something else.
>
> In contrast, a read-write lock actually has known properties, and we have
> existing locking mechanisms for those. And we call them read-write locks
> DESPITE THE FACT that the reading part can be done recursively.
>
> If you call a read-write lock a "recursive" lock, then you're a moron.
> It simply is _not_ a recursive lock. And neither is the lock you actually
> implemented, even though you (and Stephen) continually call it that.
>
> SO STOP CALLING IT A RECURSIVE LOCK. Look at your very own code: you can
> actually only use that lock in a recursive context in a _very_ specific
> place. Notice how it's only "recursive" when taken in the per-CPU context,
> but _not_ recursive when the filter-updating code ("writer") takes it?
>
> Do you understand now? It really shouldn't be so hard for you.
>
> Naming is important. Locking is important. You did both things wrong. You
> named your locks something incorrect and mis-leading that didn't actually
> describe them, and you did your own private locking code without then
> documenting what the rules for this special lock were.
>
> Maybe in your world that's ok. But no, in mine it's not. I've seen too
> many damn _non-functioning_ locks to ever want to see stuff like that
> again.
>
>

Linus,

I actually sent *one* buggy patch, and you already gave your feedback and NACK.

Fine

I even relayed this to Stephen suggesting him not calling this a recursive lock.
(Note how I use 'suggesting' here)

So, what do you want from me ? Should I copy 100 times :

"I should not call it a recursive lock. I shall not invent new locking infra. I am a moron."
"I should not call it a recursive lock. I shall not invent new locking infra. I am a moron."
"I should not call it a recursive lock. I shall not invent new locking infra. I am a moron."
"I should not call it a recursive lock. I shall not invent new locking infra. I am a moron."
"I should not call it a recursive lock. I shall not invent new locking infra. I am a moron."
"I should not call it a recursive lock. I shall not invent new locking infra. I am a moron."
...

OK done

Can we now proceed and continue ?

Thank you