Re: PATCH [1/1]: audit: acquire creds selectively to reduce atomic op overhead

David Howells
2011-03-08T18:03:07Z

Tony Jones <tonyj@suse.de> wrote:

> Commit c69e8d9c01db added calls to get_task_cred and put_cred in
> audit_filter_rules. Profiling with a large number of audit rules active on
> the exit chain shows that we are spending upto 48% in this routine for
> syscall intensive tests, most of which is in the atomic ops.
>
> The following patch acquires the cred if a rule requires it. In our
> particular case above, most rules had no cred requirement and this dropped
> the time spent in audit_filter_rules down to ~12%. An alternative would be
> for the caller to acquire the cred just once for the whole chain and pass
> into audit_filter_rules. I can create an alternate patch doing this if
> required.

There's no actual need to get a ref on the named task's creds.

If tsk == current, no locking is needed at all.

If tsk != current, the RCU read lock is sufficient. See task_cred_xxx() in
include/linux/cred.h.

Hmmm... I wonder... The audit filter uses tsk->real_cred, but is that
correct? Should it be using tsk->cred? And is tsk always going to be
current?

> + const struct cred *cred=NULL;

Binary operators like '=' should have a space on each side.

David