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SubjectRe: [PATCH] sched/debug: initialize sd_sysctl_cpus if !CONFIG_CPUMASK_OFFSTACK
On Wed, Jan 30, 2019 at 09:14:00PM +0100, Peter Zijlstra wrote:
> On Tue, Jan 29, 2019 at 10:12:45AM -0500, Masayoshi Mizuma wrote:
> > From: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>
> >
> > register_sched_domain_sysctl() copies the cpu_possible_mask into
> > sd_sysctl_cpus, but only if sd_sysctl_cpus hasn't already been
> > allocated (ie, CONFIG_CPUMASK_OFFSTACK is set). However, when
> > CONFIG_CPUMASK_OFFSTACK is not set, sd_sysctl_cpus is left uninitialized
> > (all zeroes) and the kernel may fail to initialize sched_domain sysctl
> > entries for all possible cpus.
> >
> > This is visible to the user if the kernel is booted with maxcpus=n, or
> > if ACPI tables have been modified to leave cpus offline, and then
> > checking for missing /proc/sys/kernel/sched_domain/cpu* entries.
> >
> > Fix this by separating the allocataion and initialization, and adding
> > a flag to initialize the possible cpu entries while system booting only.
> >
> > Signed-off-by: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>
> > Reviewed-by: Masayoshi Mizuma <m.mizuma@jp.fujitsu.com>
> > Tested-by: Syuuichirou Ishii <ishii.shuuichir@jp.fujitsu.com>
> > Tested-by: Tarumizu, Kohei <tarumizu.kohei@jp.fujitsu.com>
> > ---
> > kernel/sched/debug.c | 4 ++++
> > 1 file changed, 4 insertions(+)
> >
> > diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
> > index de3de997e245..9c6637f3e21d 100644
> > --- a/kernel/sched/debug.c
> > +++ b/kernel/sched/debug.c
> > @@ -310,6 +310,7 @@ static struct ctl_table *sd_alloc_ctl_cpu_table(int cpu)
> >
> > static cpumask_var_t sd_sysctl_cpus;
> > static struct ctl_table_header *sd_sysctl_header;
> > +static int register_sched_domain_sysctl_on_boot = 1;
> >
> > void register_sched_domain_sysctl(void)
> > {
> > @@ -344,9 +345,12 @@ void register_sched_domain_sysctl(void)
> > if (!cpumask_available(sd_sysctl_cpus)) {
> > if (!alloc_cpumask_var(&sd_sysctl_cpus, GFP_KERNEL))
> > return;
> > + }
> >
> > + if (register_sched_domain_sysctl_on_boot) {
> > /* init to possible to not have holes in @cpu_entries */
> > cpumask_copy(sd_sysctl_cpus, cpu_possible_mask);
> > + register_sched_domain_sysctl_on_boot = 0;
> > }
> >
> > for_each_cpu(i, sd_sysctl_cpus) {
>
> I change it like the below. By keeping the initial value 0 it can go
> into .bss instead of .data.

Great, thanks!
Should I re-post the patch as v2?

- Masa

>
> --- a/kernel/sched/debug.c
> +++ b/kernel/sched/debug.c
> @@ -315,6 +315,7 @@ void register_sched_domain_sysctl(void)
> {
> static struct ctl_table *cpu_entries;
> static struct ctl_table **cpu_idx;
> + static bool init_done = false;
> char buf[32];
> int i;
>
> @@ -344,7 +345,10 @@ void register_sched_domain_sysctl(void)
> if (!cpumask_available(sd_sysctl_cpus)) {
> if (!alloc_cpumask_var(&sd_sysctl_cpus, GFP_KERNEL))
> return;
> + }
>
> + if (!init_done) {
> + init_done = true;
> /* init to possible to not have holes in @cpu_entries */
> cpumask_copy(sd_sysctl_cpus, cpu_possible_mask);
> }

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