[PATCH v2 5/7] sched: move CPU field back into thread_info if THREAD_INFO_IN_TASK=y

[Ard Biesheuvel]

THREAD_INFO_IN_TASK moved the CPU field out of thread_info, but this
causes some issues on architectures that define raw_smp_processor_id()
in terms of this field, due to the fact that #include'ing linux/sched.h
to get at struct task_struct is problematic in terms of circular
dependencies.

Given that thread_info and task_struct are the same data structure
anyway when THREAD_INFO_IN_TASK=y, let's move it back so that having
access to the type definition of struct thread_info is sufficient to
reference the CPU number of the current task.

Note that this requires THREAD_INFO_IN_TASK's definition of the
task_thread_info() helper to be updated, as task_cpu() takes a
pointer-to-const, whereas task_thread_info() (which is used to generate
lvalues as well), needs a non-const pointer. So make it a macro instead.

Signed-off-by: Ard Biesheuvel <ardb@xxxxxxxxxx>
Acked-by: Catalin Marinas <catalin.marinas@xxxxxxx>
Acked-by: Mark Rutland <mark.rutland@xxxxxxx>
Acked-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
---
 arch/arm64/kernel/asm-offsets.c   |  1 -
 arch/arm64/kernel/head.S          |  2 +-
 arch/powerpc/kernel/asm-offsets.c |  2 +-
 arch/powerpc/kernel/smp.c         |  2 +-
 include/linux/sched.h             | 13 +------------
 kernel/sched/sched.h              |  4 ----
 6 files changed, 4 insertions(+), 20 deletions(-)

diff --git a/arch/arm64/kernel/asm-offsets.c b/arch/arm64/kernel/asm-offsets.c
index cee9f3e9f906..0bfc048221af 100644
--- a/arch/arm64/kernel/asm-offsets.c
+++ b/arch/arm64/kernel/asm-offsets.c
@@ -27,7 +27,6 @@
 int main(void)
 {
   DEFINE(TSK_ACTIVE_MM,		offsetof(struct task_struct, active_mm));
-  DEFINE(TSK_CPU,		offsetof(struct task_struct, cpu));
   BLANK();
   DEFINE(TSK_TI_CPU,		offsetof(struct task_struct, thread_info.cpu));
   DEFINE(TSK_TI_FLAGS,		offsetof(struct task_struct, thread_info.flags));
diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
index 17962452e31d..6a98f1a38c29 100644
--- a/arch/arm64/kernel/head.S
+++ b/arch/arm64/kernel/head.S
@@ -412,7 +412,7 @@ SYM_FUNC_END(__create_page_tables)
 	scs_load \tsk
 
 	adr_l	\tmp1, __per_cpu_offset
-	ldr	w\tmp2, [\tsk, #TSK_CPU]
+	ldr	w\tmp2, [\tsk, #TSK_TI_CPU]
 	ldr	\tmp1, [\tmp1, \tmp2, lsl #3]
 	set_this_cpu_offset \tmp1
 	.endm
diff --git a/arch/powerpc/kernel/asm-offsets.c b/arch/powerpc/kernel/asm-offsets.c
index e563d3222d69..e37e4546034e 100644
--- a/arch/powerpc/kernel/asm-offsets.c
+++ b/arch/powerpc/kernel/asm-offsets.c
@@ -93,7 +93,7 @@ int main(void)
 #endif /* CONFIG_PPC64 */
 	OFFSET(TASK_STACK, task_struct, stack);
 #ifdef CONFIG_SMP
-	OFFSET(TASK_CPU, task_struct, cpu);
+	OFFSET(TASK_CPU, task_struct, thread_info.cpu);
 #endif
 
 #ifdef CONFIG_LIVEPATCH
diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
index 9cc7d3dbf439..512d875b45e0 100644
--- a/arch/powerpc/kernel/smp.c
+++ b/arch/powerpc/kernel/smp.c
@@ -1223,7 +1223,7 @@ static void cpu_idle_thread_init(unsigned int cpu, struct task_struct *idle)
 	paca_ptrs[cpu]->kstack = (unsigned long)task_stack_page(idle) +
 				 THREAD_SIZE - STACK_FRAME_OVERHEAD;
 #endif
-	idle->cpu = cpu;
+	task_thread_info(idle)->cpu = cpu;
 	secondary_current = current_set[cpu] = idle;
 }
 
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 39039ce8ac4c..8699594e3f99 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -750,10 +750,6 @@ struct task_struct {
 #ifdef CONFIG_SMP
 	int				on_cpu;
 	struct __call_single_node	wake_entry;
-#ifdef CONFIG_THREAD_INFO_IN_TASK
-	/* Current CPU: */
-	unsigned int			cpu;
-#endif
 	unsigned int			wakee_flips;
 	unsigned long			wakee_flip_decay_ts;
 	struct task_struct		*last_wakee;
@@ -1886,10 +1882,7 @@ extern struct thread_info init_thread_info;
 extern unsigned long init_stack[THREAD_SIZE / sizeof(unsigned long)];
 
 #ifdef CONFIG_THREAD_INFO_IN_TASK
-static inline struct thread_info *task_thread_info(struct task_struct *task)
-{
-	return &task->thread_info;
-}
+# define task_thread_info(task)	(&(task)->thread_info)
 #elif !defined(__HAVE_THREAD_FUNCTIONS)
 # define task_thread_info(task)	((struct thread_info *)(task)->stack)
 #endif
@@ -2114,11 +2107,7 @@ static __always_inline bool need_resched(void)
 
 static inline unsigned int task_cpu(const struct task_struct *p)
 {
-#ifdef CONFIG_THREAD_INFO_IN_TASK
-	return READ_ONCE(p->cpu);
-#else
 	return READ_ONCE(task_thread_info(p)->cpu);
-#endif
 }
 
 extern void set_task_cpu(struct task_struct *p, unsigned int cpu);
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 3d3e5793e117..79fcbad11450 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1926,11 +1926,7 @@ static inline void __set_task_cpu(struct task_struct *p, unsigned int cpu)
 	 * per-task data have been completed by this moment.
 	 */
 	smp_wmb();
-#ifdef CONFIG_THREAD_INFO_IN_TASK
-	WRITE_ONCE(p->cpu, cpu);
-#else
 	WRITE_ONCE(task_thread_info(p)->cpu, cpu);
-#endif
 	p->wake_cpu = cpu;
 #endif
 }
-- 
2.30.2