linux-kernel - Re: [patch] preempt: select PREEMPT_DYNAMIC under PREEMPTION instead of PREEMPT

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Date:   Tue, 9 Feb 2021 17:19:04 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Mike Galbraith <efault@....de>
Cc:     lkml <linux-kernel@...r.kernel.org>,
        Michal Hocko <mhocko@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [patch] preempt: select PREEMPT_DYNAMIC under PREEMPTION instead
 of PREEMPT

On Tue, Feb 09, 2021 at 05:13:15PM +0100, Peter Zijlstra wrote:
> On Tue, Feb 09, 2021 at 05:05:14PM +0100, Mike Galbraith wrote:
> 
> > ld: init/main.o: in function `trace_initcall_start':
> > /backup/usr/local/src/kernel/linux-tip-rt/./include/trace/events/initcall.h:27: undefined reference to `__SCT__preempt_schedule_notrace'
> 
> Ooohh... this is because x86 can't build PREEMPT without PREEMPT_DYNAMIC
> anymore. Maybe I should fix that. Lemme see what that would take.

Does this work?

---
diff --git a/arch/x86/include/asm/preempt.h b/arch/x86/include/asm/preempt.h
index 0aa96f824af1..f8cb8af4de5c 100644
--- a/arch/x86/include/asm/preempt.h
+++ b/arch/x86/include/asm/preempt.h
@@ -110,6 +110,13 @@ extern asmlinkage void preempt_schedule_thunk(void);
 
 #define __preempt_schedule_func preempt_schedule_thunk
 
+extern asmlinkage void preempt_schedule_notrace(void);
+extern asmlinkage void preempt_schedule_notrace_thunk(void);
+
+#define __preempt_schedule_notrace_func preempt_schedule_notrace_thunk
+
+#ifdef CONFIG_PREEMPT_DYNAMIC
+
 DECLARE_STATIC_CALL(preempt_schedule, __preempt_schedule_func);
 
 #define __preempt_schedule() \
@@ -118,11 +125,6 @@ do { \
 	asm volatile ("call " STATIC_CALL_TRAMP_STR(preempt_schedule) : ASM_CALL_CONSTRAINT); \
 } while (0)
 
-extern asmlinkage void preempt_schedule_notrace(void);
-extern asmlinkage void preempt_schedule_notrace_thunk(void);
-
-#define __preempt_schedule_notrace_func preempt_schedule_notrace_thunk
-
 DECLARE_STATIC_CALL(preempt_schedule_notrace, __preempt_schedule_notrace_func);
 
 #define __preempt_schedule_notrace() \
@@ -131,6 +133,16 @@ do { \
 	asm volatile ("call " STATIC_CALL_TRAMP_STR(preempt_schedule_notrace) : ASM_CALL_CONSTRAINT); \
 } while (0)
 
-#endif
+#else /* PREEMPT_DYNAMIC */
+
+#define __preempt_schedule() \
+	asm volatile ("call preempt_schedule_thunk" : ASM_CALL_CONSTRAINT);
+
+#define __preempt_schedule_notrace() \
+	asm volatile ("call preempt_schedule_notrace_thunk" : ASM_CALL_CONSTRAINT);
+
+#endif /* PREEMPT_DYNAMIC */
+
+#endif /* PREEMPTION */
 
 #endif /* __ASM_PREEMPT_H */