linux-kernel - [PATCH 2/9] cpu/hotplug: Move idle_thread

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Message-Id: <20230201204338.1337562-3-usama.arif@bytedance.com>
Date:   Wed,  1 Feb 2023 20:43:31 +0000
From:   Usama Arif <usama.arif@...edance.com>
To:     dwmw2@...radead.org, tglx@...utronix.de
Cc:     mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
        hpa@...or.com, x86@...nel.org, pbonzini@...hat.com,
        paulmck@...nel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, rcu@...r.kernel.org, mimoja@...oja.de,
        hewenliang4@...wei.com, thomas.lendacky@....com, seanjc@...gle.com,
        pmenzel@...gen.mpg.de, fam.zheng@...edance.com,
        punit.agrawal@...edance.com, simon.evans@...edance.com,
        liangma@...ngbit.com, David Woodhouse <dwmw@...zon.co.uk>
Subject: [PATCH 2/9] cpu/hotplug: Move idle_thread_get() to <linux/smpboot.h>

From: David Woodhouse <dwmw@...zon.co.uk>

Instead of relying purely on the special-case wrapper in bringup_cpu()
to pass the idle thread to __cpu_up(), expose idle_thread_get() so that
the architecture code can obtain it directly when necessary.

This will be useful when the existing __cpu_up() is split into multiple
phases, only *one* of which will actually need the idle thread.

If the architecture code is to register its new pre-bringup states with
the cpuhp core, having a special-case wrapper to pass extra arguments is
non-trivial and it's easier just to let the arch register its function
pointer to be invoked with the standard API.

Signed-off-by: David Woodhouse <dwmw@...zon.co.uk>
---
 include/linux/smpboot.h | 7 +++++++
 kernel/smpboot.h        | 2 --
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/include/linux/smpboot.h b/include/linux/smpboot.h
index 9d1bc65d226c..3862addcaa34 100644
--- a/include/linux/smpboot.h
+++ b/include/linux/smpboot.h
@@ -5,6 +5,13 @@
 #include <linux/types.h>
 
 struct task_struct;
+
+#ifdef CONFIG_GENERIC_SMP_IDLE_THREAD
+struct task_struct *idle_thread_get(unsigned int cpu);
+#else
+static inline struct task_struct *idle_thread_get(unsigned int cpu) { return NULL; }
+#endif
+
 /* Cookie handed to the thread_fn*/
 struct smpboot_thread_data;
 
diff --git a/kernel/smpboot.h b/kernel/smpboot.h
index 34dd3d7ba40b..60c609318ad6 100644
--- a/kernel/smpboot.h
+++ b/kernel/smpboot.h
@@ -5,11 +5,9 @@
 struct task_struct;
 
 #ifdef CONFIG_GENERIC_SMP_IDLE_THREAD
-struct task_struct *idle_thread_get(unsigned int cpu);
 void idle_thread_set_boot_cpu(void);
 void idle_threads_init(void);
 #else
-static inline struct task_struct *idle_thread_get(unsigned int cpu) { return NULL; }
 static inline void idle_thread_set_boot_cpu(void) { }
 static inline void idle_threads_init(void) { }
 #endif
-- 
2.25.1