[RFC PATCH 6/8] powerpc: smp: remove hack to obtain offset of task_struct::cpu

From: Ard Biesheuvel <ardb@kernel.org>
To: linux-kernel@vger.kernel.org
Cc: Ard Biesheuvel <ardb@kernel.org>,
	Keith Packard <keithpac@amazon.com>,
	Russell King <linux@armlinux.org.uk>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Christophe Leroy <christophe.leroy@csgroup.eu>,
	Paul Mackerras <paulus@samba.org>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	Heiko Carstens <hca@linux.ibm.com>,
	Vasily Gorbik <gor@linux.ibm.com>,
	Christian Borntraeger <borntraeger@de.ibm.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	Peter Zijlstra <peterz@infradead.org>,
	Kees Cook <keescook@chromium.org>,
	Andy Lutomirski <luto@kernel.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Arnd Bergmann <arnd@arndb.de>,
	linux-arm-kernel@lists.infradead.org,
	linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org,
	linux-s390@vger.kernel.org
Subject: [RFC PATCH 6/8] powerpc: smp: remove hack to obtain offset of task_struct::cpu
Date: Tue, 14 Sep 2021 14:10:34 +0200	[thread overview]
Message-ID: <20210914121036.3975026-7-ardb@kernel.org> (raw)
In-Reply-To: <20210914121036.3975026-1-ardb@kernel.org>

Instead of relying on awful hacks to obtain the offset of the cpu field
in struct task_struct, move it back into struct thread_info, which does
not create the same level of circular dependency hell when trying to
include the header file that defines it.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
 arch/powerpc/Makefile             | 11 -----------
 arch/powerpc/include/asm/smp.h    | 17 +----------------
 arch/powerpc/kernel/asm-offsets.c |  2 --
 3 files changed, 1 insertion(+), 29 deletions(-)

diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
index aa6808e70647..54cad1faa5d0 100644
--- a/arch/powerpc/Makefile
+++ b/arch/powerpc/Makefile
@@ -446,17 +446,6 @@ else
 endif
 endif
 
-ifdef CONFIG_SMP
-ifdef CONFIG_PPC32
-prepare: task_cpu_prepare
-
-PHONY += task_cpu_prepare
-task_cpu_prepare: prepare0
-	$(eval KBUILD_CFLAGS += -D_TASK_CPU=$(shell awk '{if ($$2 == "TASK_CPU") print $$3;}' include/generated/asm-offsets.h))
-
-endif # CONFIG_PPC32
-endif # CONFIG_SMP
-
 PHONY += checkbin
 # Check toolchain versions:
 # - gcc-4.6 is the minimum kernel-wide version so nothing required.
diff --git a/arch/powerpc/include/asm/smp.h b/arch/powerpc/include/asm/smp.h
index 7ef1cd8168a0..007332a4a732 100644
--- a/arch/powerpc/include/asm/smp.h
+++ b/arch/powerpc/include/asm/smp.h
@@ -87,22 +87,7 @@ int is_cpu_dead(unsigned int cpu);
 /* 32-bit */
 extern int smp_hw_index[];
 
-/*
- * This is particularly ugly: it appears we can't actually get the definition
- * of task_struct here, but we need access to the CPU this task is running on.
- * Instead of using task_struct we're using _TASK_CPU which is extracted from
- * asm-offsets.h by kbuild to get the current processor ID.
- *
- * This also needs to be safeguarded when building asm-offsets.s because at
- * that time _TASK_CPU is not defined yet. It could have been guarded by
- * _TASK_CPU itself, but we want the build to fail if _TASK_CPU is missing
- * when building something else than asm-offsets.s
- */
-#ifdef GENERATING_ASM_OFFSETS
-#define raw_smp_processor_id()		(0)
-#else
-#define raw_smp_processor_id()		(*(unsigned int *)((void *)current + _TASK_CPU))
-#endif
+#define raw_smp_processor_id()		(current_thread_info()->cpu)
 #define hard_smp_processor_id() 	(smp_hw_index[smp_processor_id()])
 
 static inline int get_hard_smp_processor_id(int cpu)
diff --git a/arch/powerpc/kernel/asm-offsets.c b/arch/powerpc/kernel/asm-offsets.c
index e37e4546034e..cc05522f50bf 100644
--- a/arch/powerpc/kernel/asm-offsets.c
+++ b/arch/powerpc/kernel/asm-offsets.c
@@ -9,8 +9,6 @@
  * #defines from the assembly-language output.
  */
 
-#define GENERATING_ASM_OFFSETS	/* asm/smp.h */
-
 #include <linux/compat.h>
 #include <linux/signal.h>
 #include <linux/sched.h>
-- 
2.30.2


_______________________________________________
linux-riscv mailing list
linux-riscv@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-riscv
