On 2023-10-31 17:14:01 [+0100], Oliver Hartkopp wrote:

Hi Sebastian,

Hi Oliver,

The content of gwj->mod can be overwritten with new modification rules at
runtime. But this update (with memcpy) has to take place when there is no
incoming network traffic.

This is my assumption. But "no incoming network traffic" is not ensured,
right?

quoted

If not, my suggestion would be replacing the bh-off, memcpy part with:
|		old_mod = rcu_replace_pointer(gwj->mod, new_mod, true);
|		kfree_rcu_mightsleep(old_mod);

and doing the needed pointer replacement with for struct cgw_job::mod
and RCU annotation.

Replacing a pointer does not copy any data to the cf_mod structure, right?

Yes. The cf_mod data structure is embedded into cgw_job. So it would
have to become a pointer. Then cgw_create_job() would create a new
cf_mod via cgw_parse_attr() but it would be a new allocated structure
instead on stack like it is now. And then in the existing case you would
do the swap. Otherwise (non-existing, brand new) it becomes part of the
new created cgw_job.

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.

Best regards,
Oliver

Sebastian