[tip: smp/core] cpu/hotplug: Provide bringup_hibernate_cpu()

[tip-bot2 for Qais Yousef]

The following commit has been merged into the smp/core branch of tip:

Commit-ID:     d720f98604391dab6aa3cb4c1bc005ed1aba4703
Gitweb:        https://git.kernel.org/tip/d720f98604391dab6aa3cb4c1bc005ed1aba4703
Author:        Qais Yousef <qais.yousef@xxxxxxx>
AuthorDate:    Mon, 23 Mar 2020 13:51:01 
Committer:     Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitterDate: Wed, 25 Mar 2020 12:59:34 +01:00

cpu/hotplug: Provide bringup_hibernate_cpu()

arm64 uses cpu_up() in the resume from hibernation code to ensure that the
CPU on which the system hibernated is online. Provide a core function for
this.

[ tglx: Split out from the combo arm64 patch ]

Signed-off-by: Qais Yousef <qais.yousef@xxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Acked-by: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
Link: https://lkml.kernel.org/r/20200323135110.30522-9-qais.yousef@xxxxxxx

---
 include/linux/cpu.h |  1 +
 kernel/cpu.c        | 23 +++++++++++++++++++++++
 2 files changed, 24 insertions(+)

diff --git a/include/linux/cpu.h b/include/linux/cpu.h
index 64a246e..9dc1e89 100644
--- a/include/linux/cpu.h
+++ b/include/linux/cpu.h
@@ -93,6 +93,7 @@ int add_cpu(unsigned int cpu);
 void notify_cpu_starting(unsigned int cpu);
 extern void cpu_maps_update_begin(void);
 extern void cpu_maps_update_done(void);
+int bringup_hibernate_cpu(unsigned int sleep_cpu);
 
 #else	/* CONFIG_SMP */
 #define cpuhp_tasks_frozen	0
diff --git a/kernel/cpu.c b/kernel/cpu.c
index 03c7271..f803678 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -1275,6 +1275,29 @@ int add_cpu(unsigned int cpu)
 }
 EXPORT_SYMBOL_GPL(add_cpu);
 
+/**
+ * bringup_hibernate_cpu - Bring up the CPU that we hibernated on
+ * @sleep_cpu: The cpu we hibernated on and should be brought up.
+ *
+ * On some architectures like arm64, we can hibernate on any CPU, but on
+ * wake up the CPU we hibernated on might be offline as a side effect of
+ * using maxcpus= for example.
+ */
+int bringup_hibernate_cpu(unsigned int sleep_cpu)
+{
+	int ret;
+
+	if (!cpu_online(sleep_cpu)) {
+		pr_info("Hibernated on a CPU that is offline! Bringing CPU up.\n");
+		ret = cpu_up(sleep_cpu);
+		if (ret) {
+			pr_err("Failed to bring hibernate-CPU up!\n");
+			return ret;
+		}
+	}
+	return 0;
+}
+
 #ifdef CONFIG_PM_SLEEP_SMP
 static cpumask_var_t frozen_cpus;