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[PATCH 4.12 73/84] sched/topology: Fix building of overlapping sched-groups

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  [PATCH 4.12 73/84] sched/topology: Fix building of overlapping sched-groups Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-07-19 11:50 +0200

#1691219 — [PATCH 4.12 73/84] sched/topology: Fix building of overlapping sched-groups

4.12-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Peter Zijlstra <peterz@infradead.org>

commit 0372dd2736e02672ac6e189c31f7d8c02ad543cd upstream.

When building the overlapping groups, we very obviously should start
with the previous domain of _this_ @cpu, not CPU-0.

This can be readily demonstrated with a topology like:

  node   0   1   2   3
    0:  10  20  30  20
    1:  20  10  20  30
    2:  30  20  10  20
    3:  20  30  20  10

Where (for example) CPU1 ends up generating the following nonsensical groups:

  [] CPU1 attaching sched-domain:
  []  domain 0: span 0-2 level NUMA
  []   groups: 1 2 0
  []   domain 1: span 0-3 level NUMA
  []    groups: 1-3 (cpu_capacity = 3072) 0-1,3 (cpu_capacity = 3072)

Where the fact that domain 1 doesn't include a group with span 0-2 is
the obvious fail.

With patch this looks like:

  [] CPU1 attaching sched-domain:
  []  domain 0: span 0-2 level NUMA
  []   groups: 1 0 2
  []   domain 1: span 0-3 level NUMA
  []    groups: 0-2 (cpu_capacity = 3072) 0,2-3 (cpu_capacity = 3072)

Debugged-by: Lauro Ramos Venancio <lvenanci@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Fixes: e3589f6c81e4 ("sched: Allow for overlapping sched_domain spans")
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 kernel/sched/topology.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -525,7 +525,7 @@ build_overlap_sched_groups(struct sched_
 
 	cpumask_clear(covered);
 
-	for_each_cpu(i, span) {
+	for_each_cpu_wrap(i, span, cpu) {
 		struct cpumask *sg_span;
 
 		if (cpumask_test_cpu(i, covered))

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