[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@redhat.com>
Signed-off-by: Raghavendra K T <redacted>
---
 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

----- Original Message -----

From: "Raghavendra K T" <redacted>
To: mingo@redhat.com, peterz@infradead.org, benh@kernel.crashing.org, paulus@samba.org, mpe@ellerman.id.au,
anton@samba.org, akpm@linux-foundation.org
Cc: jstancek@redhat.com, gkurz@linux.vnet.ibm.com, "grant likely" <redacted>,
nikunj@linux.vnet.ibm.com, vdavydov@parallels.com, "raghavendra kt" [off-list ref],
linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, linux-mm@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@redhat.com>

Tested-by: Jan Stancek <jstancek@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

Commit-ID:  9c03ee147193645be4c186d3688232fa438c57c7
Gitweb:     http://git.kernel.org/tip/9c03ee147193645be4c186d3688232fa438c57c7
Author:     Raghavendra K T [off-list ref]
AuthorDate: Sat, 16 Jan 2016 00:31:23 +0530
Committer:  Ingo Molnar [off-list ref]
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@redhat.com>
Tested-by: Jan Stancek <jstancek@redhat.com>
Signed-off-by: Raghavendra K T <redacted>
Cc: <redacted>
Cc: <redacted>
Cc: <redacted>
Cc: <redacted>
Cc: <redacted>
Cc: <redacted>
Cc: <peterz@infradead.org>
Cc: <benh@kernel.crashing.org>
Cc: <redacted>
Cc: <mpe@ellerman.id.au>
Cc: <redacted>
Link: http://lkml.kernel.org/r/1452884483-11676-1-git-send-email-raghavendra.kt@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@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;
 

On 01/19/2016 07:08 PM, tip-bot for Raghavendra K T wrote:

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.?