Re: [tip:sched/core] sched/cputime: Refactor the cputime_adjust() code

Peter Zijlstra
2017-07-04T09:17:47Z

On Fri, Jun 30, 2017 at 06:10:35AM -0700, tip-bot for Gustavo A. R. Silva wrote:
> Commit-ID: 72298e5c92c50edd8cb7cfda4519483ce65fa166
> Gitweb: http://git.kernel.org/tip/72298e5c92c50edd8cb7cfda4519483ce65fa166
> Author: Gustavo A. R. Silva <garsilva@embeddedor.com>
> AuthorDate: Thu, 29 Jun 2017 13:41:28 -0500
> Committer: Ingo Molnar <mingo@kernel.org>
> CommitDate: Fri, 30 Jun 2017 09:37:59 +0200
>
> sched/cputime: Refactor the cputime_adjust() code
>
> Address a Coverity false positive, which is caused by overly
> convoluted code:
>
> Value assigned to variable 'utime' at line 619:utime = rtime;
> is overwritten at line 642:utime = rtime - stime; before it
> can be used. This makes such variable assignment useless.
>
> Remove this variable assignment and refactor the code related.
>
> Addresses-Coverity-ID: 1371643
> Signed-off-by: Gustavo A. R. Silva <garsilva@embeddedor.com>
> Cc: Frans Klaver <fransklaver@gmail.com>
> Cc: Frederic Weisbecker <fweisbec@gmail.com>
> Cc: Linus Torvalds <torvalds@linux-foundation.org>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Rik van Riel <riel@redhat.com>
> Cc: Stanislaw Gruszka <sgruszka@redhat.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Wanpeng Li <wanpeng.li@hotmail.com>
> Link: http://lkml.kernel.org/r/20170629184128.GA5271@embeddedgus
> Signed-off-by: Ingo Molnar <mingo@kernel.org>
> ---
> kernel/sched/cputime.c | 16 +++++-----------
> 1 file changed, 5 insertions(+), 11 deletions(-)
>
> diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
> index aea3135..67c70e2 100644
> --- a/kernel/sched/cputime.c
> +++ b/kernel/sched/cputime.c
> @@ -615,19 +615,13 @@ static void cputime_adjust(struct task_cputime *curr,
> * userspace. Once a task gets some ticks, the monotonicy code at
> * 'update' will ensure things converge to the observed ratio.
> */
> - if (stime == 0) {
> - utime = rtime;
> - goto update;
> + if (stime != 0) {
> + if (utime == 0)
> + stime = rtime;
> + else
> + stime = scale_stime(stime, rtime, stime + utime);
> }
>
> - if (utime == 0) {
> - stime = rtime;
> - goto update;
> - }
> -
> - stime = scale_stime(stime, rtime, stime + utime);
> -
> -update:
> /*
> * Make sure stime doesn't go backwards; this preserves monotonicity
> * for utime because rtime is monotonic.

Argh, no... That code was perfectly fine. The new code otoh is
convoluted crap.

It had the form:

if (exception1)
deal with exception1

if (execption2)
deal with exception2

do normal stuff

Which is as simple and straight forward as it gets.

The new code otoh reads like:

if (!exception1) {
if (exception2)
deal with exception 2
else
do normal stuff
}

which is absolute shit.

So NAK on this.