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

Christophe Leroy
2021-09-30T13:09:01Z

Le 30/09/2021 à 14:58, Ard Biesheuvel a écrit :
> 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@kernel.org>
> Acked-by: Catalin Marinas <catalin.marinas@arm.com>
> Acked-by: Mark Rutland <mark.rutland@arm.com>
> Acked-by: Michael Ellerman <mpe@ellerman.id.au>
> ---
> 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]

Why do you need to change the name ?

For powerpc64, you leave TASK_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

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