[PATCH] Fix: PowerNV crash with 4.4.0-rc8 at sched_init_numa

[Jan Stancek]

----- Original Message -----
> From: "Raghavendra K T" <raghavendra.kt at linux.vnet.ibm.com>
> To: mingo at redhat.com, peterz at infradead.org, benh at kernel.crashing.org, paulus at samba.org, mpe at ellerman.id.au,
> anton at samba.org, akpm at linux-foundation.org
> Cc: jstancek at redhat.com, gkurz at linux.vnet.ibm.com, "grant likely" <grant.likely at linaro.org>,
> nikunj at linux.vnet.ibm.com, vdavydov at parallels.com, "raghavendra kt" <raghavendra.kt at linux.vnet.ibm.com>,
> linuxppc-dev at lists.ozlabs.org, linux-kernel at vger.kernel.org, linux-mm at kvack.org
> Sent: Friday, 15 January, 2016 8:01:23 PM
> Subject: [PATCH] Fix: PowerNV crash with 4.4.0-rc8 at sched_init_numa
> 
> Commit c118baf80256 ("arch/powerpc/mm/numa.c: do not allocate bootmem
> memory for non existing nodes") avoided bootmem memory allocation for
> non existent nodes.
> 
> When DEBUG_PER_CPU_MAPS enabled, powerNV system failed to boot because
> in sched_init_numa, cpumask_or operation was done on unallocated nodes.
> Fix that by making cpumask_or operation only on existing nodes.
> 
> [ Tested with and w/o DEBUG_PER_CPU_MAPS on x86 and powerpc ]
> 
> Reported-by: Jan Stancek <jstancek at redhat.com>

Tested-by: Jan Stancek <jstancek at redhat.com>

I also verified with my setup, that this made the crash go away.
Report mail thread for reference:
  https://lists.ozlabs.org/pipermail/linuxppc-dev/2016-January/137691.html

Regards,
Jan

> Signed-off-by: Raghavendra K T <raghavendra.kt at linux.vnet.ibm.com>
> ---
>  kernel/sched/core.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 44253ad..474658b 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -6840,7 +6840,7 @@ static void sched_init_numa(void)
>  
>  			sched_domains_numa_masks[i][j] = mask;
>  
> -			for (k = 0; k < nr_node_ids; k++) {
> +			for_each_node(k) {
>  				if (node_distance(j, k) > sched_domains_numa_distance[i])
>  					continue;
>  
> --
> 1.7.11.7
> 
>