[PATCH v2 6/7] powerpc: smp: remove hack to obtain offset of task_struct::cpu

Ard Biesheuvel
2021-09-30T12:59:18Z

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>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Michael Ellerman <mpe@ellerman.id.au>
---
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