From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755891AbbGTHgx (ORCPT ); Mon, 20 Jul 2015 03:36:53 -0400 Received: from mail-wi0-f177.google.com ([209.85.212.177]:38014 "EHLO mail-wi0-f177.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755511AbbGTHgv (ORCPT ); Mon, 20 Jul 2015 03:36:51 -0400 Date: Mon, 20 Jul 2015 09:36:47 +0200 From: Ingo Molnar To: Olof Johansson Cc: will.deacon@arm.com, catalin.marinas@arm.com, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Dave Hansen Subject: Re: [PATCH] arm64: Minor refactoring of cpu_switch_to() to fix build breakage Message-ID: <20150720073647.GA10504@gmail.com> References: <1437359377-39932-1-git-send-email-olof@lixom.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1437359377-39932-1-git-send-email-olof@lixom.net> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Olof Johansson wrote: > Commit 0c8c0f03e3a2 ("x86/fpu, sched: Dynamically allocate 'struct fpu'") > moved the thread_struct to the bottom of task_struct. As a result, the > offset is now too large to be used in an immediate add on arm64 with > some kernel configs: > > arch/arm64/kernel/entry.S: Assembler messages: > arch/arm64/kernel/entry.S:588: Error: immediate out of range > arch/arm64/kernel/entry.S:597: Error: immediate out of range > > There's really no reason for cpu_switch_to to take a task_struct pointer > in the first place, since all it does is access the thread.cpu_context > member. So, just pass that in directly. > > Fixes: 0c8c0f03e3a2 ("x86/fpu, sched: Dynamically allocate 'struct fpu'") > Cc: Dave Hansen > Signed-off-by: Olof Johansson > --- > arch/arm64/include/asm/processor.h | 4 ++-- > arch/arm64/kernel/asm-offsets.c | 2 -- > arch/arm64/kernel/entry.S | 34 ++++++++++++++++------------------ > arch/arm64/kernel/process.c | 3 ++- > 4 files changed, 20 insertions(+), 23 deletions(-) So why not pass in 'thread_struct' as the patch below does - it looks much simpler to me. This way the assembly doesn't have to be changed at all. Thanks, Ingo =====================================> * Guenter wrote: > On Sat, Jul 18, 2015 at 04:27:17PM -0700, Guenter wrote: > > Hi, > > > > Commit 0c8c0f03e3a2 ("x86/fpu, sched: Dynamically allocate 'struct fpu'") > > causes s390 builds in mainline to fail as follows. > > > > arch/s390/kernel/traps.c: Assembler messages: > > arch/s390/kernel/traps.c:262: Error: operand out of range > > (0x00000000000023e8 is not between 0x0000000000000000 and 0x0000000000000fff) > > arch/s390/kernel/traps.c:300: Error: operand out of range > > (0x00000000000023e8 is not between 0x0000000000000000 and 0x0000000000000fff) > > > > Also: > > arm64:allmodconfig: > > arch/arm64/kernel/entry.S: Assembler messages: > arch/arm64/kernel/entry.S:588: Error: immediate out of range > arch/arm64/kernel/entry.S:597: Error: immediate out of range > make[1]: *** [arch/arm64/kernel/entry.o] Error 1 > > I didn't bisect that one, but it looks like the cause is the same. Hm, it looks like the new, increased offset of 'thread_struct' within 'task_struct' goes over a limit that these instructions are able to support on arm64: arch/arm64/kernel/asm-offsets.c: DEFINE(THREAD_CPU_CONTEXT, offsetof(struct task_struct, thread.cpu_context)); arch/arm64/kernel/entry.S: add x8, x0, #THREAD_CPU_CONTEXT arch/arm64/kernel/entry.S: add x8, x1, #THREAD_CPU_CONTEXT If there's no instruction that can support such offset sizes then I suspect the straightforward fix would be to pass in thread_struct instead - like the patch below. That's a tiny bit cleaner for type encapsulation anyway. Warning: it's not even build tested, but in case it works: Signed-off-by: Ingo Molnar Thanks, Ingo ================ arch/arm64/include/asm/processor.h | 4 ++-- arch/arm64/kernel/asm-offsets.c | 2 +- arch/arm64/kernel/process.c | 2 +- 3 files changed, 4 insertions(+), 4 deletions(-) diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h index e4c893e54f01..890f84bb3b8c 100644 --- a/arch/arm64/include/asm/processor.h +++ b/arch/arm64/include/asm/processor.h @@ -152,8 +152,8 @@ static inline void cpu_relax(void) #define cpu_relax_lowlatency() cpu_relax() /* Thread switching */ -extern struct task_struct *cpu_switch_to(struct task_struct *prev, - struct task_struct *next); +extern struct task_struct *cpu_switch_to(struct thread_struct *prev, + struct thread_struct *next); #define task_pt_regs(p) \ ((struct pt_regs *)(THREAD_START_SP + task_stack_page(p)) - 1) diff --git a/arch/arm64/kernel/asm-offsets.c b/arch/arm64/kernel/asm-offsets.c index c99701a34d7b..3785373c2369 100644 --- a/arch/arm64/kernel/asm-offsets.c +++ b/arch/arm64/kernel/asm-offsets.c @@ -39,7 +39,7 @@ int main(void) DEFINE(TI_TASK, offsetof(struct thread_info, task)); DEFINE(TI_CPU, offsetof(struct thread_info, cpu)); BLANK(); - DEFINE(THREAD_CPU_CONTEXT, offsetof(struct task_struct, thread.cpu_context)); + DEFINE(THREAD_CPU_CONTEXT, offsetof(struct thread_struct, cpu_context)); BLANK(); DEFINE(S_X0, offsetof(struct pt_regs, regs[0])); DEFINE(S_X1, offsetof(struct pt_regs, regs[1])); diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c index 223b093c9440..436e95bda1b2 100644 --- a/arch/arm64/kernel/process.c +++ b/arch/arm64/kernel/process.c @@ -325,7 +325,7 @@ struct task_struct *__switch_to(struct task_struct *prev, dsb(ish); /* the actual thread switch */ - last = cpu_switch_to(prev, next); + last = cpu_switch_to(&prev.thread, &next.thread); return last; }