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SubjectRe: [PATCH] sched/vtime: Fix an unitialized variable warning
On Fri, Mar 27, 2020 at 10:43:34PM +0100, Borislav Petkov wrote:
> Hi dude,
>
> right before I was going to send the trivial, shut-up-gcc variant, I
> thought that maybe we should do this instead.
>
> Thoughts?
>
> ---
> Fix:
>
> kernel/sched/cputime.c: In function ‘kcpustat_field’:
> kernel/sched/cputime.c:1007:6: warning: ‘val’ may be used \
> uninitialized in this function [-Wmaybe-uninitialized]
> 1007 | u64 val;
> | ^~~
>
> because gcc can't see that val is used only when err is 0.
>
> Signed-off-by: Borislav Petkov <bp@suse.de>
> ---
> kernel/sched/cputime.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
> index dac9104d126f..ff9435dee1df 100644
> --- a/kernel/sched/cputime.c
> +++ b/kernel/sched/cputime.c
> @@ -1003,12 +1003,12 @@ u64 kcpustat_field(struct kernel_cpustat *kcpustat,
> enum cpu_usage_stat usage, int cpu)
> {
> u64 *cpustat = kcpustat->cpustat;
> + u64 val = cpustat[usage];
> struct rq *rq;
> - u64 val;
> int err;
>
> if (!vtime_accounting_enabled_cpu(cpu))
> - return cpustat[usage];
> + return val;
>
> rq = cpu_rq(cpu);


Hurph.. this might result in an unconditional load (and extra
cache-miss) for the vtime_accounting_enabled_cpu() case.

I suspesct the =0 this would be better. Stupid stupid compiler!

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