From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 1153B4A14 for ; Mon, 26 Sep 2022 23:55:43 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id B0758C43148 for ; Mon, 26 Sep 2022 23:55:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1664236543; bh=3oWBp5OuNgMk4osp9P8nypPw1Pry43XjuA12xTaf6Ak=; h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=Q+3y1fZVt2CGEGfpERpVE/yGjAX+Q/+EktIKab/h9I7bSZeiCveYzq7/QHfIz4yj8 QyOTxGJ4Ba82eaie2j8xzJ1PiuWq8KGDThO+Eb//aB3WEjyI91j+ex2vLRvmv4qliI gYabKf4lS2MBZgyQXs8ezO0CuByHzfI9RAUL3LVq/boVIyRb047Jo1mb1FgORoN4fI TYuLq9Bjj46lY0THdKqEOfOaktRRlbGo1azMhjy0Fwo1BgdKqKHZU3z5NcB3n79uL9 L4BzLoH+GthPQ//1qCbKnfxXjYn4ASrzDZvJzj3aMgiW1YpIrt4W/lxICeFtP/Bm82 8jlqimysawzaw== Received: by mail-ot1-f45.google.com with SMTP id r22-20020a9d7516000000b00659ef017e34so5425361otk.13 for ; Mon, 26 Sep 2022 16:55:43 -0700 (PDT) X-Gm-Message-State: ACrzQf1aAZFXhgq5L+A9TPoFE3ChNhqEVnggXUTXG21yzt6s7PKhfyCa xVq3yWKu09E3sdkoZboiOSA3g4Tzo4kLuuH5h/8= X-Google-Smtp-Source: AMsMyM4f+D6DvJ/+x2of0iu+4OrOFy9HHMiCsEQmpdrH1/bZ+CR9gVfL7hSG/foSTOwrT+0d+IevqmOtrzL8lQnAWdc= X-Received: by 2002:a9d:37b6:0:b0:65c:abc:c1d7 with SMTP id x51-20020a9d37b6000000b0065c0abcc1d7mr5909560otb.308.1664236542750; Mon, 26 Sep 2022 16:55:42 -0700 (PDT) Precedence: bulk X-Mailing-List: llvm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 References: <20220925175356.681-1-jszhang@kernel.org> <20220925175356.681-3-jszhang@kernel.org> In-Reply-To: From: Guo Ren Date: Tue, 27 Sep 2022 07:55:27 +0800 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH 2/4] riscv: consolidate ret_from_kernel_thread into ret_from_fork To: Jisheng Zhang Cc: Paul Walmsley , Palmer Dabbelt , Albert Ou , Nathan Chancellor , Nick Desaulniers , linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, llvm@lists.linux.dev Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Tue, Sep 27, 2022 at 12:14 AM Jisheng Zhang 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 wrot= e: > > > > > > 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 > > > --- > > > 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=3D0 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 =3D gp_in_global; > > /* Supervisor/Machine, irqs on: */ > > childregs->status =3D SR_PP | SR_PIE; > > > > p->thread.ra =3D (unsigned long)ret_from_kernel_thread; > > p->thread.s[0] =3D (unsigned long)args->fn; > > p->thread.s[1] =3D (unsigned long)args->fn_arg; > > } else { > > *childregs =3D *(current_pt_regs()); > > ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Oh, I'm wrong, It's switch_to_restore -> exception_restore. > > if (usp) /* User fork */ > > childregs->sp =3D usp; > > if (clone_flags & CLONE_SETTLS) > > childregs->tp =3D tls; > > childregs->a0 =3D 0; /* Return value of fork() */ > > p->thread.ra =3D (unsigned long)ret_from_fork; > > } > > p->thread.sp =3D (unsigned long)childregs; /* kernel sp */ > > > > > > > > @@ -182,8 +180,9 @@ int copy_thread(struct task_struct *p, const stru= ct kernel_clone_args *args) > > > if (clone_flags & CLONE_SETTLS) > > > childregs->tp =3D tls; > > > childregs->a0 =3D 0; /* Return value of fork() */ > > > - p->thread.ra =3D (unsigned long)ret_from_fork; > > > + p->thread.s[0] =3D 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 impl= icit. =E2=9E=9C 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_for= k 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: =E2=9E=9C 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 =3D 0. > > Thanks --=20 Best Regards Guo Ren