Messages in this thread |  | | From | Guo Ren <> | Date | Tue, 27 Sep 2022 07:55:27 +0800 | Subject | Re: [PATCH 2/4] riscv: consolidate ret_from_kernel_thread into ret_from_fork |
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On Tue, Sep 27, 2022 at 12:14 AM Jisheng Zhang <jszhang@kernel.org> wrote: > > On Mon, Sep 26, 2022 at 07:25:30AM +0800, Guo Ren wrote: > > On Mon, Sep 26, 2022 at 2:03 AM Jisheng Zhang <jszhang@kernel.org> wrote: > > > > > > The ret_from_kernel_thread() behaves similarly with ret_from_fork(), > > > the only difference is whether call the fn(arg) or not, this can be > > > acchieved by testing fn is NULL or not, I.E s0 is 0 or not. > > > > > > Signed-off-by: Jisheng Zhang <jszhang@kernel.org> > > > --- > > > arch/riscv/kernel/entry.S | 11 +++-------- > > > arch/riscv/kernel/process.c | 5 ++--- > > > 2 files changed, 5 insertions(+), 11 deletions(-) > > > > > > diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S > > > index 2207cf44a3bc..a3e1ed2fa2ac 100644 > > > --- a/arch/riscv/kernel/entry.S > > > +++ b/arch/riscv/kernel/entry.S > > > @@ -323,20 +323,15 @@ END(handle_kernel_stack_overflow) > > > > > > ENTRY(ret_from_fork) > > > call schedule_tail > > > - move a0, sp /* pt_regs */ > > > - la ra, ret_from_exception > > > - tail syscall_exit_to_user_mode > > > -ENDPROC(ret_from_fork) > > > - > > > -ENTRY(ret_from_kernel_thread) > > > - call schedule_tail > > > + beqz s0, 1f /* not from kernel thread */ > > Hi Guo, > > > We can't use s0 as condition for ret_from_fork/ret_from_kernel_thread. > > The s0=0 is also okay for ret_from_fork. > > IIUC, in ret_from_fork, the s0 comes p->thread.s[0] rather than s0 in > pt_regs. Yes, you are correct.
> > > > > /* p->thread holds context to be restored by __switch_to() */ > > if (unlikely(args->fn)) { > > /* Kernel thread */ > > memset(childregs, 0, sizeof(struct pt_regs)); > > childregs->gp = gp_in_global; > > /* Supervisor/Machine, irqs on: */ > > childregs->status = SR_PP | SR_PIE; > > > > p->thread.ra = (unsigned long)ret_from_kernel_thread; > > p->thread.s[0] = (unsigned long)args->fn; > > p->thread.s[1] = (unsigned long)args->fn_arg; > > } else { > > *childregs = *(current_pt_regs()); > > ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Oh, I'm wrong, It's switch_to_restore -> exception_restore.
> > if (usp) /* User fork */ > > childregs->sp = usp; > > if (clone_flags & CLONE_SETTLS) > > childregs->tp = tls; > > childregs->a0 = 0; /* Return value of fork() */ > > p->thread.ra = (unsigned long)ret_from_fork; > > } > > p->thread.sp = (unsigned long)childregs; /* kernel sp */ > > > > <snip> > > > > @@ -182,8 +180,9 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args) > > > if (clone_flags & CLONE_SETTLS) > > > childregs->tp = tls; > > > childregs->a0 = 0; /* Return value of fork() */ > > > - p->thread.ra = (unsigned long)ret_from_fork; > > > + p->thread.s[0] = 0; > > Here we assign 0 to p->thread.s[0] I missed that.
Merge thread & fork is not a good idea, and using fp as the flag is so implicit.
➜ linux git:(rv64sv32) grep ret_from_fork arch -r | grep entry.S arch/arc/kernel/entry.S:ENTRY(ret_from_fork) arch/arc/kernel/entry.S:END(ret_from_fork) arch/csky/kernel/entry.S:ENTRY(ret_from_fork) arch/x86/kernel/process_32.c: * the task-switch, and shows up in ret_from_fork in entry.S, arch/alpha/kernel/entry.S: .globl ret_from_fork arch/alpha/kernel/entry.S: .ent ret_from_fork arch/alpha/kernel/entry.S:ret_from_fork: arch/alpha/kernel/entry.S:.end ret_from_fork arch/loongarch/kernel/entry.S:SYM_CODE_START(ret_from_fork) arch/loongarch/kernel/entry.S:SYM_CODE_END(ret_from_fork) arch/hexagon/kernel/vm_entry.S: .globl ret_from_fork arch/hexagon/kernel/vm_entry.S:ret_from_fork: arch/microblaze/kernel/entry.S: (copy_thread makes ret_from_fork the return address in each new thread's arch/microblaze/kernel/entry.S:C_ENTRY(ret_from_fork): arch/m68k/kernel/entry.S:ENTRY(ret_from_fork) arch/arm64/kernel/entry.S:SYM_CODE_START(ret_from_fork) arch/arm64/kernel/entry.S:SYM_CODE_END(ret_from_fork) arch/arm64/kernel/entry.S:NOKPROBE(ret_from_fork) arch/riscv/kernel/entry.S:ENTRY(ret_from_fork) arch/riscv/kernel/entry.S:ENDPROC(ret_from_fork) arch/s390/kernel/entry.S:# a new process exits the kernel with ret_from_fork arch/s390/kernel/entry.S:ENTRY(ret_from_fork) arch/s390/kernel/entry.S: brasl %r14,__ret_from_fork arch/s390/kernel/entry.S:ENDPROC(ret_from_fork) arch/mips/kernel/entry.S:FEXPORT(ret_from_fork) arch/openrisc/kernel/entry.S: /* All syscalls return here... just pay attention to ret_from_fork arch/openrisc/kernel/entry.S:ENTRY(ret_from_fork) arch/openrisc/kernel/entry.S: * that may be either schedule(), ret_from_fork(), or arch/nios2/kernel/entry.S:ENTRY(ret_from_fork) arch/xtensa/kernel/entry.S:ENTRY(ret_from_fork) arch/xtensa/kernel/entry.S:ENDPROC(ret_from_fork) arch/sparc/kernel/entry.S: .globl ret_from_fork arch/sparc/kernel/entry.S:ret_from_fork: ➜ linux git:(rv64sv32) grep ret_from_kernel_thread arch -r | grep entry.S arch/csky/kernel/entry.S:ENTRY(ret_from_kernel_thread) arch/alpha/kernel/entry.S: .globl ret_from_kernel_thread arch/alpha/kernel/entry.S: .ent ret_from_kernel_thread arch/alpha/kernel/entry.S:ret_from_kernel_thread: arch/alpha/kernel/entry.S:.end ret_from_kernel_thread arch/parisc/kernel/entry.S:ENTRY(ret_from_kernel_thread) arch/parisc/kernel/entry.S:END(ret_from_kernel_thread) arch/loongarch/kernel/entry.S:SYM_CODE_START(ret_from_kernel_thread) arch/loongarch/kernel/entry.S:SYM_CODE_END(ret_from_kernel_thread) arch/microblaze/kernel/entry.S:C_ENTRY(ret_from_kernel_thread): arch/m68k/kernel/entry.S:ENTRY(ret_from_kernel_thread) arch/riscv/kernel/entry.S:ENTRY(ret_from_kernel_thread) arch/riscv/kernel/entry.S:ENDPROC(ret_from_kernel_thread) arch/mips/kernel/entry.S:FEXPORT(ret_from_kernel_thread) arch/openrisc/kernel/entry.S: * ret_from_kernel_thread(). If we are returning to a new thread, arch/nios2/kernel/entry.S:ENTRY(ret_from_kernel_thread) arch/xtensa/kernel/entry.S:ENTRY(ret_from_kernel_thread) arch/xtensa/kernel/entry.S:ENDPROC(ret_from_kernel_thread) arch/sparc/kernel/entry.S: .globl ret_from_kernel_thread arch/sparc/kernel/entry.S:ret_from_kernel_thread:
Many architectures use a similar style. If you want to continue the patch, I think you should first rename ret_from_fork properly, and give an explicit flag definition, not just setting fp = 0.
> > Thanks
-- Best Regards Guo Ren
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