> We found that when auditing is disabled using "auditctl -D", that
> there's still a significant overhead when doing syscalls. This overhead
> is not present when a single never rule is inserted using "auditctl -a
> task,never".
>
> Using Anton's null syscall microbenchmark from
>
http://ozlabs.org/~anton/junkcode/null_syscall.c we currently have on a
> powerpc machine:
>
> # auditctl -D
> No rules
> # ./null_syscall
> null_syscall: 739.03 cycles 100.00%
> # auditctl -a task,never
> # ./null_syscall
> null_syscall: 204.63 cycles 100.00%
>
> This doesn't seem right, as we'd hope that auditing would have the same
> minimal impact when disabled via -D as when we have a single never rule.
>
> The patch below creates a fast path when initialising a task. If the
> rules list for tasks is empty (the disabled -D option), we mark auditing
> as disabled for this task.
>
> When this is applied, our null syscall benchmark improves in the
> disabled case to match the single never rule case.
>
> # auditctl -D
> No rules
> # ./null_syscall
> null_syscall: 204.62 cycles 100.00%
> # auditctl -a task,never
> # ./null_syscall
> null_syscall: 204.63 cycles 100.00%
>
> Reported-by: Anton Blanchard <anton@samba.org>
> Signed-off-by: Michael Neuling <mikey@neuling.org>
> ---
> I'm not familiar with the auditing code/infrastructure so I may have
> misunderstood something here
>
> diff --git a/kernel/auditsc.c b/kernel/auditsc.c
> index 1b31c13..1cd6ec7 100644
> --- a/kernel/auditsc.c
> +++ b/kernel/auditsc.c
> @@ -666,6 +666,11 @@ static enum audit_state audit_filter_task(struct task_struct *tsk, char **key)
> enum audit_state state;
>
> rcu_read_lock();
> + /* Fast path. If the list is empty, disable auditing */
> + if (list_empty(&audit_filter_list[AUDIT_FILTER_TASK])) {
> + rcu_read_unlock();
> + return AUDIT_DISABLED;
> + }
> list_for_each_entry_rcu(e, &audit_filter_list[AUDIT_FILTER_TASK], list) {
> if (audit_filter_rules(tsk, &e->rule, NULL, NULL, &state)) {
> if (state == AUDIT_RECORD_CONTEXT)
