Re: [PATCH] fs/exec.c: Add fast path for ENOENT on PATH search before allocating mm

Kees Cook
2023-11-07T22:50:05Z

On Tue, Nov 07, 2023 at 10:23:16PM +0100, Mateusz Guzik wrote:
> If the patch which dodges second lookup still somehow appears slower a
> flamegraph or other profile would be nice. I can volunteer to take a
> look at what's going on provided above measurements will be done and
> show funkyness.

When I looked at this last, it seemed like all the work done in
do_filp_open() (my patch, which moved the lookup earlier) was heavier
than the duplicate filename_lookup().

What I didn't test was moving the sched_exec() before the mm creation,
which Peter confirmed shouldn't be a problem, but I think that might be
only a tiny benefit, if at all.

If you can do some comparisons, that would be great; it always takes me
a fair bit of time to get set up for flame graph generation, etc. :)

-Kees

--
Kees Cook