Currently, task_struct is defined in <linux/sched.h>, which (indirectly) pulls in a number of low-level arch headers such as <asm/preempt.h> through a number of other headers. Thus, code and structures in these headers can't rely on the definition of task_struct. Some of these headers are necessary for the definition of task_struct, so moving task_struct into its own header is insufficient tio avoid circular includes.
With CONFIG_THREAD_INFO_IN_TASK, arch code needs to implement its own get_current() for the generic get_thread_info(). To avoid header dependency issues, this relies on thread_info being the first member of task_struct. This can be used by low-level arch code, as it doesn't depend on the definition of task_struct. For architectures without preempt-safe this_cpu ops, some data required by low-level arch code (e.g. preempt_count) has to be stored per-thread, and for the reasons above, we cannot place this in task_struct (or thread_struct, since we cannot know its offset from within task_struct). The only practical location for these is thread_info. This patch allows architectures with CONFIG_ARCH_HAS_OWN_THREAD_INFO to define their own thread_info, avoiding the problems described above. Signed-off-by: Mark Rutland <[email protected]> Cc: Andrew Morton <[email protected]> Cc: Andy Lutomirski <[email protected]> Cc: Catalin Marinas <[email protected]> Cc: Kees Cook <[email protected]> Cc: Will Deacon <[email protected]> Cc: [email protected] --- include/linux/thread_info.h | 3 ++- init/Kconfig | 3 +++ 2 files changed, 5 insertions(+), 1 deletion(-) diff --git a/include/linux/thread_info.h b/include/linux/thread_info.h index d9622f7..7984f87 100644 --- a/include/linux/thread_info.h +++ b/include/linux/thread_info.h @@ -13,7 +13,8 @@ struct timespec; struct compat_timespec; -#ifdef CONFIG_THREAD_INFO_IN_TASK +#if defined(CONFIG_THREAD_INFO_IN_TASK) && \ + !defined(CONFIG_ARCH_HAS_OWN_THREAD_INFO) struct thread_info { u32 flags; /* low level flags */ }; diff --git a/init/Kconfig b/init/Kconfig index 3b9a47f..f812098 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -26,6 +26,9 @@ config IRQ_WORK config BUILDTIME_EXTABLE_SORT bool +config ARCH_HAS_OWN_THREAD_INFO + bool + config THREAD_INFO_IN_TASK bool help -- 1.9.1
