linux-kernel - Re: [tip:sched/urgent] sched: Fix crash in sched_init

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Message-ID: <56B87E32.4050003@linux.vnet.ibm.com>
Date:	Mon, 08 Feb 2016 17:08:26 +0530
From:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
To:	tglx@...utronix.de, mingo@...nel.org, linux-mm@...ck.org,
	mpe@...erman.id.au, hpa@...or.com, nikunj@...ux.vnet.ibm.com,
	linuxppc-dev@...ts.ozlabs.org, peterz@...radead.org,
	vdavydov@...allels.com, gkurz@...ux.vnet.ibm.com,
	linux-kernel@...r.kernel.org, raghavendra.kt@...ux.vnet.ibm.com,
	jstancek@...hat.com, benh@...nel.crashing.org, anton@...ba.org,
	grant.likely@...aro.org, paulus@...ba.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org
CC:	tip-bot for Raghavendra K T <tipbot@...or.com>,
	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:sched/urgent] sched: Fix crash in sched_init_numa()

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@...ux.vnet.ibm.com>
> AuthorDate: Sat, 16 Jan 2016 00:31:23 +0530
> Committer:  Ingo Molnar <mingo@...nel.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@...hat.com>
> Tested-by: Jan Stancek <jstancek@...hat.com>
> Signed-off-by: Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
> Cc: <gkurz@...ux.vnet.ibm.com>
> Cc: <grant.likely@...aro.org>
> Cc: <nikunj@...ux.vnet.ibm.com>
> Cc: <vdavydov@...allels.com>
> Cc: <linuxppc-dev@...ts.ozlabs.org>
> Cc: <linux-mm@...ck.org>
> Cc: <peterz@...radead.org>
> Cc: <benh@...nel.crashing.org>
> Cc: <paulus@...ba.org>
> Cc: <mpe@...erman.id.au>
> Cc: <anton@...ba.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@...nel.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.?