Re: [RFC PATCH 1/3] LoongArch: Implement CONFIG_THREAD_INFO_IN_TASK

[Tiezhu Yang]

On 2026/6/3 下午10:24, Huacai Chen wrote:
> On Wed, Jun 3, 2026 at 10:30 AM Tiezhu Yang <yangtiezhu@xxxxxxxxxxx> wrote:

...

> > For static structures like init_task, any uninitialized fields are
> > automatically zeroed out by the compiler according to the C standard.
> > Stripping away dozens of lines of ".field = 0" complies with modern
> > Linux kernel code-cleaning standards. It makes the macro much shorter
> > and highlights the only field that actually requires a special
> > runtime value (the kernel stack top in .reg03).
> I know it is the same for compilers, I mean the current way gives more
> information for humans.
>
> In addition, without reg02, this piece completely has no relationship
> with CONFIG_THREAD_INFO_IN_TASK, so please drop it.

Do you mean keep the original INIT_THREAD as is? No any changes for it?
".reg03 = (unsigned long)&init_stack + sizeof(init_stack)," is not
necessary?

That is to say, do not modify arch/loongarch/include/asm/processor.h?

> > For reference, please see how INIT_THREAD is defined in other major
> > architectures, where they only initialize what is strictly necessary:

...

> None of these commits remove current_pt_regs. Some of them has no
> current_pt_regs before THREAD_INFO_IN_TASK, and ARM32 still has its
> own implementations in arch/arm/include/asm/ptrace.h now which is
> nearly the same as LoongArch.

If you think it should keep current_pt_regs() as is, I am OK, will do
it in the next version.

That is to say, do not modify arch/loongarch/include/asm/ptrace.h?

> > > >    /* Helpers for working with the user stack pointer */

...

> set_current() is a very good friend of get_current(). Though "$tp" is
> enough for get_current(), from the x86 implementation we know that it
> can also get from the per-cpu array (but suboptimal).
>
> Move set_current() to current.h also don't need to include
> <linux/percpu.h> and <linux/sched.h>, it only need to forwarding
> declare "task_struct" and include <asm/percpu.h>, which is exactly
> done in the x86 implementation.
>
> And you needn't worry about the compiling, I have tested before I comment.

If you think this is proper, I am OK.

Replace __entry_task with current_task (x86) or cpu_tasks (uml)?
Replace entry_task_switch() with set_current()? or something else?
It seems a little strange for the following code in smp.c:

diff --git a/arch/loongarch/kernel/smp.c b/arch/loongarch/kernel/smp.c
index 4b74409a98a3..3afdeca7bc2a 100644
--- a/arch/loongarch/kernel/smp.c
+++ b/arch/loongarch/kernel/smp.c
@@ -665,7 +665,7 @@ asmlinkage void start_secondary(void)
        set_my_cpu_offset(per_cpu_offset(cpu));

        cpu_probe();
-       entry_task_switch(current);
+       set_current(current);
        constant_clockevent_init();
        loongson_init_secondary();

Thanks,
Tiezhu