From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-15.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 38FF6C433DB for ; Wed, 17 Mar 2021 18:37:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DD08E64F51 for ; Wed, 17 Mar 2021 18:37:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232716AbhCQShM (ORCPT ); Wed, 17 Mar 2021 14:37:12 -0400 Received: from mail.kernel.org ([198.145.29.99]:58370 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229601AbhCQSgl (ORCPT ); Wed, 17 Mar 2021 14:36:41 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 6611664E61; Wed, 17 Mar 2021 18:36:39 +0000 (UTC) Date: Wed, 17 Mar 2021 18:36:36 +0000 From: Catalin Marinas To: Chen Jun Cc: linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, akpm@linux-foundation.org, will@kernel.org, rui.xiang@huawei.com, Mark Brown Subject: Re: [PATCH 2/2] arm64: stacktrace: Add skip when task == current Message-ID: <20210317183636.GG12269@arm.com> References: <20210317142050.57712-1-chenjun102@huawei.com> <20210317142050.57712-3-chenjun102@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210317142050.57712-3-chenjun102@huawei.com> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Mar 17, 2021 at 02:20:50PM +0000, Chen Jun wrote: > On ARM64, cat /sys/kernel/debug/page_owner, all pages return the same > stack: > stack_trace_save+0x4c/0x78 > register_early_stack+0x34/0x70 > init_page_owner+0x34/0x230 > page_ext_init+0x1bc/0x1dc > > The reason is that: > check_recursive_alloc always return 1 because that > entries[0] is always equal to ip (__set_page_owner+0x3c/0x60). > > The root cause is that: > commit 5fc57df2f6fd ("arm64: stacktrace: Convert to ARCH_STACKWALK") > make the save_trace save 2 more entries. > > Add skip in arch_stack_walk when task == current. > > Fixes: 5fc57df2f6fd ("arm64: stacktrace: Convert to ARCH_STACKWALK") > Signed-off-by: Chen Jun > --- > arch/arm64/kernel/stacktrace.c | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c > index ad20981..c26b0ac 100644 > --- a/arch/arm64/kernel/stacktrace.c > +++ b/arch/arm64/kernel/stacktrace.c > @@ -201,11 +201,12 @@ void arch_stack_walk(stack_trace_consume_fn consume_entry, void *cookie, > > if (regs) > start_backtrace(&frame, regs->regs[29], regs->pc); > - else if (task == current) > + else if (task == current) { > + ((struct stacktrace_cookie *)cookie)->skip += 2; > start_backtrace(&frame, > (unsigned long)__builtin_frame_address(0), > (unsigned long)arch_stack_walk); > - else > + } else > start_backtrace(&frame, thread_saved_fp(task), > thread_saved_pc(task)); I don't like abusing the cookie here. It's void * as it's meant to be an opaque type. I'd rather skip the first two frames in walk_stackframe() instead before invoking fn(). Prior to the conversion to ARCH_STACKWALK, we were indeed skipping two more entries in __save_stack_trace() if tsk == current. Something like below, completely untested: diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c index ad20981dfda4..2a9f759aa41a 100644 --- a/arch/arm64/kernel/stacktrace.c +++ b/arch/arm64/kernel/stacktrace.c @@ -115,10 +115,15 @@ NOKPROBE_SYMBOL(unwind_frame); void notrace walk_stackframe(struct task_struct *tsk, struct stackframe *frame, bool (*fn)(void *, unsigned long), void *data) { + /* for the current task, we don't want this function nor its caller */ + int skip = tsk == current ? 2 : 0; + while (1) { int ret; - if (!fn(data, frame->pc)) + if (skip) + skip--; + else if (!fn(data, frame->pc)) break; ret = unwind_frame(tsk, frame); if (ret < 0) -- Catalin