netdev - Re: [RFC] Questionable RCU/BH usage in cgw_create

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Date: Thu, 30 Nov 2023 20:56:26 +0100
From: Oliver Hartkopp <socketcan@...tkopp.net>
To: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc: Marc Kleine-Budde <mkl@...gutronix.de>, linux-can@...r.kernel.org,
 netdev@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [RFC] Questionable RCU/BH usage in cgw_create_job().

Hi Sebastian,

On 30.11.23 17:43, Sebastian Andrzej Siewior wrote:
> On 2023-10-31 17:52:47 [+0100], To Oliver Hartkopp wrote:

>> The point is to replace/ update cf_mod at runtime while following RCU
>> rules so always either new or the old object is observed. Never an
>> intermediate step.
> 
> Do you want me to take care of it?

Yes, sorry.

In fact I've searched some time what would fit best without getting a 
clear picture.

As the changes triggered by the netlink update should come into action 
with the next processed CAN frame I have thought about adding a shadow 
'mod' structure which is written instantly.
And then a flag could be set, that is switched by the next incoming CAN 
frame.

I just would have a problem with performing some memory allocation for 
the 'mod' updates which might take some unpredictable time.

If you have some cool ideas please let me know. I'm unsure what is the 
most effective and performant approach for this use case.

Many thanks,
Oliver