linux-kernel - [PATCH v2 2/5] smp: add set_nr_cpu

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Date:   Mon,  5 Sep 2022 16:08:17 -0700
From:   Yury Norov <yury.norov@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     Yury Norov <yury.norov@...il.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Valentin Schneider <vschneid@...hat.com>,
        Sander Vanheule <sander@...nheule.net>,
        Alexey Klimov <klimov.linux@...il.com>,
        Eric Biggers <ebiggers@...gle.com>
Subject: [PATCH v2 2/5] smp: add set_nr_cpu_ids()

In preparation to support compile-time nr_cpu_ids, add a setter for
the variable.

This is a no-op for all arches.

Signed-off-by: Yury Norov <yury.norov@...il.com>
---
 arch/loongarch/kernel/setup.c | 2 +-
 arch/mips/kernel/setup.c      | 2 +-
 arch/x86/kernel/smpboot.c     | 4 ++--
 arch/x86/xen/smp_pv.c         | 2 +-
 include/linux/cpumask.h       | 5 +++++
 kernel/smp.c                  | 4 ++--
 6 files changed, 12 insertions(+), 7 deletions(-)

diff --git a/arch/loongarch/kernel/setup.c b/arch/loongarch/kernel/setup.c
index 8f5c2f9a1a83..18a81edd3ac5 100644
--- a/arch/loongarch/kernel/setup.c
+++ b/arch/loongarch/kernel/setup.c
@@ -346,7 +346,7 @@ static void __init prefill_possible_map(void)
 	for (; i < NR_CPUS; i++)
 		set_cpu_possible(i, false);
 
-	nr_cpu_ids = possible;
+	set_nr_cpu_ids(possible);
 }
 #endif
 
diff --git a/arch/mips/kernel/setup.c b/arch/mips/kernel/setup.c
index 2ca156a5b231..e8a0759cb4d0 100644
--- a/arch/mips/kernel/setup.c
+++ b/arch/mips/kernel/setup.c
@@ -750,7 +750,7 @@ static void __init prefill_possible_map(void)
 	for (; i < NR_CPUS; i++)
 		set_cpu_possible(i, false);
 
-	nr_cpu_ids = possible;
+	set_nr_cpu_ids(possible);
 }
 #else
 static inline void prefill_possible_map(void) {}
diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index f24227bc3220..3f3ea0287f69 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -1316,7 +1316,7 @@ static void __init smp_sanity_check(void)
 			nr++;
 		}
 
-		nr_cpu_ids = 8;
+		set_nr_cpu_ids(8);
 	}
 #endif
 
@@ -1569,7 +1569,7 @@ __init void prefill_possible_map(void)
 		possible = i;
 	}
 
-	nr_cpu_ids = possible;
+	set_nr_cpu_ids(possible);
 
 	pr_info("Allowing %d CPUs, %d hotplug CPUs\n",
 		possible, max_t(int, possible - num_processors, 0));
diff --git a/arch/x86/xen/smp_pv.c b/arch/x86/xen/smp_pv.c
index ba7af2eca755..480be82e9b7b 100644
--- a/arch/x86/xen/smp_pv.c
+++ b/arch/x86/xen/smp_pv.c
@@ -179,7 +179,7 @@ static void __init _get_smp_config(unsigned int early)
 	 * hypercall to expand the max number of VCPUs an already
 	 * running guest has. So cap it up to X. */
 	if (subtract)
-		nr_cpu_ids = nr_cpu_ids - subtract;
+		set_nr_cpu_ids(nr_cpu_ids - subtract);
 #endif
 
 }
diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
index bd047864c7ac..0588bfe350d4 100644
--- a/include/linux/cpumask.h
+++ b/include/linux/cpumask.h
@@ -39,6 +39,11 @@ typedef struct cpumask { DECLARE_BITMAP(bits, NR_CPUS); } cpumask_t;
 #define nr_cpu_ids		1U
 #else
 extern unsigned int nr_cpu_ids;
+
+static inline void set_nr_cpu_ids(unsigned int nr)
+{
+	nr_cpu_ids = nr;
+}
 #endif
 
 #ifdef CONFIG_CPUMASK_OFFSTACK
diff --git a/kernel/smp.c b/kernel/smp.c
index e971c9626a1b..150310a0947a 100644
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -1070,7 +1070,7 @@ static int __init nrcpus(char *str)
 	int nr_cpus;
 
 	if (get_option(&str, &nr_cpus) && nr_cpus > 0 && nr_cpus < nr_cpu_ids)
-		nr_cpu_ids = nr_cpus;
+		set_nr_cpu_ids(nr_cpus);
 
 	return 0;
 }
@@ -1097,7 +1097,7 @@ EXPORT_SYMBOL(nr_cpu_ids);
 /* An arch may set nr_cpu_ids earlier if needed, so this would be redundant */
 void __init setup_nr_cpu_ids(void)
 {
-	nr_cpu_ids = find_last_bit(cpumask_bits(cpu_possible_mask),NR_CPUS) + 1;
+	set_nr_cpu_ids(find_last_bit(cpumask_bits(cpu_possible_mask), NR_CPUS) + 1);
 }
 
 /* Called by boot processor to activate the rest. */
-- 
2.34.1