[PATCH 2/4] powerpc/64s: Use dec_mm_active_cpus helper

[Nicholas Piggin <npiggin@gmail.com>]

Avoid open-coded atomic_dec on mm->context.active_cpus and use the
function made for it. Add CONFIG_DEBUG_VM underflow checking on the
counter.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
 arch/powerpc/include/asm/book3s/64/mmu.h | 2 +-
 arch/powerpc/include/asm/mmu_context.h   | 1 +
 arch/powerpc/mm/book3s64/radix_tlb.c     | 2 +-
 3 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/include/asm/book3s/64/mmu.h b/arch/powerpc/include/asm/book3s/64/mmu.h
index 570a4960cf17..5cf0e9c953b3 100644
--- a/arch/powerpc/include/asm/book3s/64/mmu.h
+++ b/arch/powerpc/include/asm/book3s/64/mmu.h
@@ -261,7 +261,7 @@ static inline void radix_init_pseries(void) { }
 #define arch_clear_mm_cpumask_cpu(cpu, mm)				\
 	do {								\
 		if (cpumask_test_cpu(cpu, mm_cpumask(mm))) {		\
-			atomic_dec(&(mm)->context.active_cpus);		\
+			dec_mm_active_cpus(mm);				\
 			cpumask_clear_cpu(cpu, mm_cpumask(mm));		\
 		}							\
 	} while (0)
diff --git a/arch/powerpc/include/asm/mmu_context.h b/arch/powerpc/include/asm/mmu_context.h
index 57f5017111f4..37bffa0f7918 100644
--- a/arch/powerpc/include/asm/mmu_context.h
+++ b/arch/powerpc/include/asm/mmu_context.h
@@ -127,6 +127,7 @@ static inline void inc_mm_active_cpus(struct mm_struct *mm)
 
 static inline void dec_mm_active_cpus(struct mm_struct *mm)
 {
+	VM_WARN_ON_ONCE(atomic_read(&mm->context.active_cpus) <= 0);
 	atomic_dec(&mm->context.active_cpus);
 }
 
diff --git a/arch/powerpc/mm/book3s64/radix_tlb.c b/arch/powerpc/mm/book3s64/radix_tlb.c
index 90953cf9f648..8160c1630c3d 100644
--- a/arch/powerpc/mm/book3s64/radix_tlb.c
+++ b/arch/powerpc/mm/book3s64/radix_tlb.c
@@ -808,7 +808,7 @@ void exit_lazy_flush_tlb(struct mm_struct *mm, bool always_flush)
 	 * that's what the caller expects.
 	 */
 	if (cpumask_test_cpu(cpu, mm_cpumask(mm))) {
-		atomic_dec(&mm->context.active_cpus);
+		dec_mm_active_cpus(mm);
 		cpumask_clear_cpu(cpu, mm_cpumask(mm));
 		always_flush = true;
 	}
-- 
2.40.1