[tip:sched/urgent] sched: Fix crash in sched_init_numa()

[Raghavendra K T]

On 01/19/2016 07:08 PM, tip-bot for Raghavendra K T wrote:
> Commit-ID:  9c03ee147193645be4c186d3688232fa438c57c7
> Gitweb:     http://git.kernel.org/tip/9c03ee147193645be4c186d3688232fa438c57c7
> Author:     Raghavendra K T <raghavendra.kt at linux.vnet.ibm.com>
> AuthorDate: Sat, 16 Jan 2016 00:31:23 +0530
> Committer:  Ingo Molnar <mingo at kernel.org>
> CommitDate: Tue, 19 Jan 2016 08:42:20 +0100
>
> sched: Fix crash in sched_init_numa()
>
> The following PowerPC commit:
>
>    c118baf80256 ("arch/powerpc/mm/numa.c: do not allocate bootmem memory for non existing nodes")
>
> avoids allocating bootmem memory for non existent nodes.
>
> But when DEBUG_PER_CPU_MAPS=y is enabled, my 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=y on x86 and PowerPC. ]
>
> Reported-by: Jan Stancek <jstancek at redhat.com>
> Tested-by: Jan Stancek <jstancek at redhat.com>
> Signed-off-by: Raghavendra K T <raghavendra.kt at linux.vnet.ibm.com>
> Cc: <gkurz at linux.vnet.ibm.com>
> Cc: <grant.likely at linaro.org>
> Cc: <nikunj at linux.vnet.ibm.com>
> Cc: <vdavydov at parallels.com>
> Cc: <linuxppc-dev at lists.ozlabs.org>
> Cc: <linux-mm at kvack.org>
> Cc: <peterz at infradead.org>
> Cc: <benh at kernel.crashing.org>
> Cc: <paulus at samba.org>
> Cc: <mpe at ellerman.id.au>
> Cc: <anton at samba.org>
> Link: http://lkml.kernel.org/r/1452884483-11676-1-git-send-email-raghavendra.kt@linux.vnet.ibm.com
> Signed-off-by: Ingo Molnar <mingo at kernel.org>
> ---
>   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;
>
>
>
>

Hello Greg,
Above commit fixes the debug kernel crash in 4.4 kernel [ when
DEBUG_PER_CPU_MAPS=y to be precise]. This is a regression in 4.4 from
4.3 and should be ideally present in 4.4-stable.

Could you please pull in this change.?