Re: [PATCH] sched/debug: initialize sd_sysctl_cpus if !CONFIG_CPUMASK_OFFSTACK

[Joe Lawrence]

On 1/31/19 8:44 AM, Masayoshi Mizuma wrote:
> 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@xxxxxxxxxxxxxx>
> > >
> > > 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@xxxxxxxxxxxxxx>
> > > Reviewed-by: Masayoshi Mizuma <m.mizuma@xxxxxxxxxxxxxx>
> > > Tested-by: Syuuichirou Ishii <ishii.shuuichir@xxxxxxxxxxxxxx>
> > > Tested-by: Tarumizu, Kohei <tarumizu.kohei@xxxxxxxxxxxxxx>
> > > ---
> > >   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

Peter's revision tests fine on my aarch64 box and would get my ACK, 
however it ends up getting re-posted :)

Thanks,

-- Joe

> > --- 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);
> >   	}


-- Joe