Re: [PATCH v2 5/7] sched: move CPU field back into thread_info if THREAD_INFO_IN_TASK=y
From: Christophe Leroy
Date: Thu Sep 30 2021 - 09:22:25 EST
Le 30/09/2021 à 15:12, Ard Biesheuvel a écrit :
On Thu, 30 Sept 2021 at 15:09, Christophe Leroy
<christophe.leroy@xxxxxxxxxx> wrote:
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@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]
Why do you need to change the name ?
For powerpc64, you leave TASK_CPU.
Because arm64 has a clear idiom here, where TSK_TI_ is used for
thread_info fields accessed via a task_struct pointer. Also, it only
occurs once in the code.
Power does not seem to have this idiom, and TASK_CPU is used in many
more places, so I don't think it makes sense to change its name.
In the old days it was called TI_CPU, was changed by commit f7354ccac844
("powerpc/32: Remove CURRENT_THREAD_INFO and rename TI_CPU") after
commit ed1cd6deb013 ("powerpc: Activate CONFIG_THREAD_INFO_IN_TASK")
I don't have a strong opinion about it but we have:
$ git grep thread_info arch/powerpc/kernel/asm-offsets.c
arch/powerpc/kernel/asm-offsets.c:#include <asm/thread_info.h>
arch/powerpc/kernel/asm-offsets.c: OFFSET(TI_livepatch_sp,
thread_info, livepatch_sp);
arch/powerpc/kernel/asm-offsets.c: OFFSET(TI_LOCAL_FLAGS,
thread_info, local_flags);
arch/powerpc/kernel/asm-offsets.c:
offsetof(struct task_struct, thread_info));
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
...