Messages in this thread | | | From | Ard Biesheuvel <> | Subject | [PATCH v2 0/7] Move task_struct::cpu back into thread_info | Date | Thu, 30 Sep 2021 14:58:06 +0200 |
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Commit c65eacbe290b ("sched/core: Allow putting thread_info into task_struct") mentions that, along with moving thread_info into task_struct, the cpu field is moved out of the former into the latter, as at that point, it was the intention to ultimately get rid of thread_info entirely, but this never happened.
While collaborating with Keith on adding THREAD_INFO_IN_TASK support to ARM, we noticed that keeping CPU in task_struct is problematic for architectures that define raw_smp_processor_id() in terms of this field, as it requires linux/sched.h to be included, which causes a lot of pain in terms of circular dependencies (or 'header soup', as the original commit refers to it).
For examples of how existing architectures work around this, please refer to patches #6 or #7. In the former case, it uses an awful asm-offsets hack to index thread_info/current without using its type definition. The latter approach simply keeps a copy of the task_struct CPU field in thread_info, and keeps it in sync at context switch time.
We also discussed introducing yet another Kconfig symbol to indicate that the arch has THREAD_INFO_IN_TASK enabled but still prefers to keep its CPU field in thread_info, but simply keeping it in thread_info in all cases seems to be the cleanest approach here, so that is what this series implements.
Changes since v1/RFC: - use macro for task_thread_info() to work around constness of task_cpu()'s task_struct argument - add various acks - drop patch #8 for ARM - it was preliminary in the RFC, and it can be taken as a fix in the ARM tree once THREAD_INFO_IN_TASK actually lands.
Code can be found here: https://git.kernel.org/pub/scm/linux/kernel/git/ardb/linux.git/log/?h=move-task-cpu-to-ti-v2
Cc: Keith Packard <keithpac@amazon.com> Cc: Russell King <linux@armlinux.org.uk> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Will Deacon <will@kernel.org> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Christophe Leroy <christophe.leroy@csgroup.eu> Cc: Paul Mackerras <paulus@samba.org> Cc: Paul Walmsley <paul.walmsley@sifive.com> Cc: Palmer Dabbelt <palmer@dabbelt.com> Cc: Albert Ou <aou@eecs.berkeley.edu> Cc: Heiko Carstens <hca@linux.ibm.com>
Ard Biesheuvel (7): arm64: add CPU field to struct thread_info x86: add CPU field to struct thread_info s390: add CPU field to struct thread_info powerpc: add CPU field to struct thread_info sched: move CPU field back into thread_info if THREAD_INFO_IN_TASK=y powerpc: smp: remove hack to obtain offset of task_struct::cpu riscv: rely on core code to keep thread_info::cpu updated
arch/arm64/include/asm/thread_info.h | 1 + arch/arm64/kernel/asm-offsets.c | 2 +- arch/arm64/kernel/head.S | 2 +- arch/powerpc/Makefile | 11 ----------- arch/powerpc/include/asm/smp.h | 17 +---------------- arch/powerpc/include/asm/thread_info.h | 3 +++ arch/powerpc/kernel/asm-offsets.c | 4 +--- arch/powerpc/kernel/smp.c | 2 +- arch/riscv/kernel/asm-offsets.c | 1 - arch/riscv/kernel/entry.S | 5 ----- arch/riscv/kernel/head.S | 1 - arch/s390/include/asm/thread_info.h | 1 + arch/x86/include/asm/thread_info.h | 3 +++ include/linux/sched.h | 13 +------------ kernel/sched/sched.h | 4 ---- 15 files changed, 14 insertions(+), 56 deletions(-)
-- 2.30.2
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