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Date:   Fri, 20 Nov 2020 12:57:56 +1000
From:   Nicholas Piggin <>
Cc:     Nicholas Piggin <>,
        "Aneesh Kumar K.V" <>,
        Anton Vorontsov <>,
        Peter Zijlstra <>,
        Thomas Gleixner <>,
Subject: [PATCH 1/2] kernel/cpu: add arch override for clear_tasks_mm_cpumask() mm handling

powerpc keeps a counter in the mm which counts bits set in mm_cpumask as
well as other things. This means it can't use generic code to clear bits
out of the mask and doesn't adjust the arch specific counter.

Add an arch override allowing powerpc to use clear_tasks_mm_cpumask().

Signed-off-by: Nicholas Piggin <>
 kernel/cpu.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/kernel/cpu.c b/kernel/cpu.c
index 6ff2578ecf17..2b8d7a5db383 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -815,6 +815,10 @@ void __init cpuhp_threads_init(void)
+#ifndef arch_clear_mm_cpumask_cpu
+#define arch_clear_mm_cpumask_cpu(cpu, mm) cpumask_clear_cpu(cpu, mm_cpumask(mm))
  * clear_tasks_mm_cpumask - Safely clear tasks' mm_cpumask for a CPU
  * @cpu: a CPU id
@@ -850,7 +854,7 @@ void clear_tasks_mm_cpumask(int cpu)
 		t = find_lock_task_mm(p);
 		if (!t)
-		cpumask_clear_cpu(cpu, mm_cpumask(t->mm));
+		arch_clear_mm_cpumask_cpu(cpu, t->mm);

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