Re: [RFCv3 05/15] tcp: authopt: Add crypto initialization

[Eric Dumazet]

On 8/24/21 2:34 PM, Leonard Crestez wrote:
> The crypto_shash API is used in order to compute packet signatures. The
> API comes with several unfortunate limitations:
> 
> 1) Allocating a crypto_shash can sleep and must be done in user context.
> 2) Packet signatures must be computed in softirq context
> 3) Packet signatures use dynamic "traffic keys" which require exclusive
> access to crypto_shash for crypto_setkey.
> 
> The solution is to allocate one crypto_shash for each possible cpu for
> each algorithm at setsockopt time. The per-cpu tfm is then borrowed from
> softirq context, signatures are computed and the tfm is returned.
> 
> The pool for each algorithm is reference counted, initialized at
> setsockopt time and released in tcp_authopt_key_info's rcu callback
> 
>

I don't know, why should we really care and try so hard to release
the tfm per cpu ?

I would simply allocate them at boot time.
This would avoid the expensive refcounting (potential false sharing)