linux-kernel - Re: [tip:sched/core 3/19] kernel/sched/fair.c:7263 find_energy_efficient_cpu() error: uninitialized symbol 'util

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Date:   Sat, 12 Nov 2022 17:47:05 +0000
From:   Qais Yousef <qyousef@...alina.io>
To:     Dan Carpenter <error27@...il.com>
Cc:     oe-kbuild@...ts.linux.dev, Qais Yousef <qais.yousef@....com>,
        lkp@...el.com, oe-kbuild-all@...ts.linux.dev,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [tip:sched/core 3/19] kernel/sched/fair.c:7263
 find_energy_efficient_cpu() error: uninitialized symbol 'util_min'.

On 11/12/22 13:16, Dan Carpenter wrote:
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git sched/core
> head:   52b33d87b9197c51e8ffdc61873739d90dd0a16f
> commit: 244226035a1f9b2b6c326e55ae5188fab4f428cb [3/19] sched/uclamp: Fix fits_capacity() check in feec()
> config: riscv-randconfig-m031-20221111
> compiler: riscv64-linux-gcc (GCC) 12.1.0
> 
> If you fix the issue, kindly add following tag where applicable
> | Reported-by: kernel test robot <lkp@...el.com>
> | Reported-by: Dan Carpenter <error27@...il.com>
> 
> smatch warnings:
> kernel/sched/fair.c:7263 find_energy_efficient_cpu() error: uninitialized symbol 'util_min'.
> kernel/sched/fair.c:7263 find_energy_efficient_cpu() error: uninitialized symbol 'util_max'.
> 
> vim +/util_min +7263 kernel/sched/fair.c

[...]

> util_min/max not initialized if uclamp_is_used() is false.  (I thought
> I had reported this earlier but I don't see it on vger).

Thanks Dan!

It's harmless since util_min/max are ignored in util_fits_cpu() too;
uclamp_is_used() is checked there as well.

I couldn't reproduce, I need to get GCC 12.1.0, but the below ought to cure it.
Let me test it a bit more and send a patch.

Thanks

--
Qais Yousef

--->8---

idiff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 4cc56c91e06e..89dadaafc1ec 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -7217,10 +7217,10 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
        eenv_task_busy_time(&eenv, p, prev_cpu);
 
        for (; pd; pd = pd->next) {
+               unsigned long util_min = p_util_min, util_max = p_util_max;
                unsigned long cpu_cap, cpu_thermal_cap, util;
                unsigned long cur_delta, max_spare_cap = 0;
                unsigned long rq_util_min, rq_util_max;
-               unsigned long util_min, util_max;
                unsigned long prev_spare_cap = 0;
                int max_spare_cap_cpu = -1;
                unsigned long base_energy;
@@ -7258,10 +7258,7 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
                         * aligned with sched_cpu_util().
                         */
                        if (uclamp_is_used()) {
-                               if (uclamp_rq_is_idle(cpu_rq(cpu))) {
-                                       util_min = p_util_min;
-                                       util_max = p_util_max;
-                               } else {
+                               if (!uclamp_rq_is_idle(cpu_rq(cpu))) {
                                        /*
                                         * Open code uclamp_rq_util_with() except for
                                         * the clamp() part. Ie: apply max aggregation