Re: [RFC v3 3/6] can: make struct proto const

On Tue, Mar 15, 2011 at 10:28:13PM +0100, Oliver Hartkopp wrote:

On 14.03.2011 18:17, Kurt Van Dijck wrote:

quoted

On Mon, Mar 14, 2011 at 05:42:23PM +0100, Eric Dumazet wrote:

quoted

Le lundi 14 mars 2011 à 16:02 +0100, Kurt Van Dijck a écrit :

quoted

I see your point.
The reason I modified this was, as described, checkpatch.pl was complaining.
Anyway, this sequence was protected by a spinlock 'proto_tab_lock'.
I don't think it was a race.

Did I miss something?

As soon as proto_tab[proto] = cp; is done, another thread on another cpu
can read the pointer and follow it.

Hmm, I missed can_create() also uses the spinlock protection, so you're
probably right.

It seems a bit overkill :(
phonet uses RCU for example.

Hello Eric,

the RCU code in phonet is worth to consider. But loading and removing of
protocols is far away from being a hot path ... what would be the advantages
to move to RCU here?

Does RCU avoid a spinlock?

quoted

I'll keep that in mind.
Switching CAN protos to RCU is far beyond to goal of this patch :-)

Anyway making the struct proto a const (and set the default defines in the CAN
protocols) is a nice cleanup. Let's wait for the feedback about the RCU from
Eric ... then this patch could be put into mainline independently from the
j1939 protocol.

ack.

Kurt
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