From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754193AbbJPMw3 (ORCPT ); Fri, 16 Oct 2015 08:52:29 -0400 Received: from mail-pa0-f46.google.com ([209.85.220.46]:33578 "EHLO mail-pa0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754124AbbJPMw2 convert rfc822-to-8bit (ORCPT ); Fri, 16 Oct 2015 08:52:28 -0400 Subject: Re: [PATCH] arm64: Synchonise dump_backtrace() with perf callchain Mime-Version: 1.0 (Apple Message framework v1283) Content-Type: text/plain; charset=us-ascii From: Jungseok Lee In-Reply-To: <20151015172600.GD19202@arm.com> Date: Fri, 16 Oct 2015 21:52:21 +0900 Cc: catalin.marinas@arm.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, AKASHI Takahiro , James Morse , Mark Rutland Content-Transfer-Encoding: 8BIT Message-Id: References: <1444915314-13649-1-git-send-email-jungseoklee85@gmail.com> <20151015172600.GD19202@arm.com> To: Will Deacon X-Mailer: Apple Mail (2.1283) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Oct 16, 2015, at 2:26 AM, Will Deacon wrote: Hi Will, > On Thu, Oct 15, 2015 at 01:21:54PM +0000, Jungseok Lee wrote: >> dump_backtrace() has its own backtrace logic unlike perf callchain which >> relies on walk_stackframe(). They behave differently when a symbol is >> recorded. Perf writes it down *before* calling unwind_frame(), but >> dump_backtrace() prints it out *after* unwind_frame(). As a result, the >> last valid symbol is not added to a list in case of dump_backtrace(). >> >> This patch catches up the last symbol as synchronising dump_backtrace() >> with perf callchain. However, the patch does not cover a case where MMU >> is disabled. That is, a physical address can be stored in stack frame, >> but it's not handled. For example, a swapper process falls into this case. >> Unlike a swapper from a secondary core, a swapper on a boot cpu, which >> starting from __mmap_switched(), can't be tracked down with a simple >> conversion, phys_to_virt(), because PC is retrieved from LR - 4, not LR. > > It would be good to have an example backtrace before and after this patch > is applied, to show what it fixes. Agreed. I will add a call trace data to the commit message. >> It is a big tradeoff to change both head.S and unwind_frame() structure >> for a few of symbols in *.S, so this hunk does not take care of the case. >> >> Cc: AKASHI Takahiro >> Cc: James Morse >> Cc: Mark Rutland >> Signed-off-by: Jungseok Lee >> --- >> arch/arm64/kernel/traps.c | 16 +++++++++++----- >> 1 file changed, 11 insertions(+), 5 deletions(-) >> >> diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c >> index f93aae5..4ddb928 100644 >> --- a/arch/arm64/kernel/traps.c >> +++ b/arch/arm64/kernel/traps.c >> @@ -103,12 +103,13 @@ static void dump_mem(const char *lvl, const char *str, unsigned long bottom, >> set_fs(fs); >> } >> >> -static void dump_backtrace_entry(unsigned long where, unsigned long stack) >> +static void dump_backtrace_entry(unsigned long where) >> { >> + /* >> + * The highest stack frame of a swapper process stores PC in a form >> + * of physical address, but this case is not handled. >> + */ >> print_ip_sym(where); >> - if (in_exception_text(where)) >> - dump_mem("", "Exception stack", stack, >> - stack + sizeof(struct pt_regs), false); >> } >> >> static void dump_instr(const char *lvl, struct pt_regs *regs) >> @@ -172,12 +173,17 @@ static void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk) >> pr_emerg("Call trace:\n"); >> while (1) { >> unsigned long where = frame.pc; >> + unsigned long stack; >> int ret; >> >> + dump_backtrace_entry(where); >> ret = unwind_frame(&frame); >> if (ret < 0) >> break; >> - dump_backtrace_entry(where, frame.sp); >> + stack = frame.sp; >> + if (in_exception_text(where)) >> + dump_mem("", "Exception stack", stack, >> + stack + sizeof(struct pt_regs), false); > > AFAICT, the original code is all based on unwind_backtrace in > arch/arm/kernel/unwind.c. Does that need updating too (as a separate patch)? I think so, but I don't have any evidence from a real hardware.. Best Regards Jungseok Lee