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 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 220B9C433F5 for ; Tue, 30 Nov 2021 20:31:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:Date: Message-ID:From:References:Cc:To:Subject:Reply-To:Content-ID: Content-Description:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc :Resent-Message-ID:List-Owner; bh=FVGH9uTgtiiiDD8dnnp/ieoF7WdPFf9pqNTOoZendgY=; b=OisZ6Yan+NID8Io2Adv2iiaSBS 4/ZeGn3z86cT0SIBUODQ4l/eSaOHHi/q7zTsEe4mHgwrqRu0Pu/DpNFlLpnFNhqcla4KIw2fwYPuf WFQKYgZj9VMnzufVqSt3YIQA5Br0ETuEeocMK4k2kcQXoBbu4yi9Xe6Ru8avbfwV/ymziwLA4Mn/J MKcEc0YvNjXdA8SCZWpiIEh/9Usp4gJVfUTOW4s3w7riOBbxCWDcVzzIxmsmwwSJ3NDDXZw0B5itv Kooc6W9lOiNtqRnz/pqpmoXoUq7TPwYzvP6lMPCi7r/jrxsPE/YlHkZKexZO72TWd4DtsKHxu2ByR LVmxwU+Q==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1ms9l6-006eFe-Kt; Tue, 30 Nov 2021 20:29:48 +0000 Received: from linux.microsoft.com ([13.77.154.182]) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1ms9l2-006eEx-Ml for linux-arm-kernel@lists.infradead.org; Tue, 30 Nov 2021 20:29:46 +0000 Received: from [192.168.254.32] (unknown [47.187.212.181]) by linux.microsoft.com (Postfix) with ESMTPSA id AB08E20E0BF5; Tue, 30 Nov 2021 12:29:42 -0800 (PST) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com AB08E20E0BF5 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1638304183; bh=KMYdOA5W994MfaMzGGsxrsM8UC6AC7x5PsgboSj4d2w=; h=Subject:To:Cc:References:From:Date:In-Reply-To:From; b=daz2y9pu6vonfEhSN1JCd/nrFYhs9gAcVb5T07HpeliZ2DBqswIiiyb6wgADAPghN eeHS6JP5EQWbvKJXcbwGxUYXGNIkFSW7x5s/UitiCeieP1eaGjM2kv/CYQfMoQEkn5 8CyEYQEeJFKw7vXJRVQRvlXaxk+8NJnEha/ZxTVo= Subject: Re: [PATCH v11 1/5] arm64: Call stack_backtrace() only from within walk_stackframe() To: Mark Rutland Cc: broonie@kernel.org, jpoimboe@redhat.com, ardb@kernel.org, nobuta.keiya@fujitsu.com, sjitindarsingh@gmail.com, catalin.marinas@arm.com, will@kernel.org, jmorris@namei.org, linux-arm-kernel@lists.infradead.org, live-patching@vger.kernel.org, linux-kernel@vger.kernel.org References: <8b861784d85a21a9bf08598938c11aff1b1249b9> <20211123193723.12112-1-madvenka@linux.microsoft.com> <20211123193723.12112-2-madvenka@linux.microsoft.com> From: "Madhavan T. Venkataraman" Message-ID: <1dffea0a-fd99-ccd6-625f-c5e573186741@linux.microsoft.com> Date: Tue, 30 Nov 2021 14:29:41 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.14.0 MIME-Version: 1.0 In-Reply-To: Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20211130_122944_893556_F9674EE8 X-CRM114-Status: GOOD ( 29.74 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 11/30/21 12:29 PM, Mark Rutland wrote: > On Tue, Nov 30, 2021 at 11:13:28AM -0600, Madhavan T. Venkataraman wrote: >> On 11/30/21 9:05 AM, Mark Rutland wrote: >>> On Tue, Nov 23, 2021 at 01:37:19PM -0600, madvenka@linux.microsoft.com wrote: >>>> From: "Madhavan T. Venkataraman" >>>> >>>> Currently, arch_stack_walk() calls start_backtrace() and walk_stackframe() >>>> separately. There is no need to do that. Instead, call start_backtrace() >>>> from within walk_stackframe(). In other words, walk_stackframe() is the only >>>> unwind function a consumer needs to call. > >>>> @@ -143,15 +140,19 @@ static int notrace unwind_frame(struct task_struct *tsk, >>>> NOKPROBE_SYMBOL(unwind_frame); >>>> >>>> static void notrace walk_stackframe(struct task_struct *tsk, >>>> - struct stackframe *frame, >>>> + unsigned long fp, unsigned long pc, >>>> bool (*fn)(void *, unsigned long), void *data) >>>> { >>>> + struct stackframe frame; >>>> + >>>> + start_backtrace(&frame, fp, pc); >>>> + >>>> while (1) { >>>> int ret; >>>> >>>> - if (!fn(data, frame->pc)) >>>> + if (!fn(data, frame.pc)) >>>> break; >>>> - ret = unwind_frame(tsk, frame); >>>> + ret = unwind_frame(tsk, &frame); >>>> if (ret < 0) >>>> break; >>>> } >>>> @@ -195,17 +196,19 @@ noinline notrace void arch_stack_walk(stack_trace_consume_fn consume_entry, >>>> void *cookie, struct task_struct *task, >>>> struct pt_regs *regs) >>>> { >>>> - struct stackframe frame; >>>> - >>>> - if (regs) >>>> - start_backtrace(&frame, regs->regs[29], regs->pc); >>>> - else if (task == current) >>>> - start_backtrace(&frame, >>>> - (unsigned long)__builtin_frame_address(1), >>>> - (unsigned long)__builtin_return_address(0)); >>>> - else >>>> - start_backtrace(&frame, thread_saved_fp(task), >>>> - thread_saved_pc(task)); >>>> - >>>> - walk_stackframe(task, &frame, consume_entry, cookie); >>>> + unsigned long fp, pc; >>>> + >>>> + if (regs) { >>>> + fp = regs->regs[29]; >>>> + pc = regs->pc; >>>> + } else if (task == current) { >>>> + /* Skip arch_stack_walk() in the stack trace. */ >>>> + fp = (unsigned long)__builtin_frame_address(1); >>>> + pc = (unsigned long)__builtin_return_address(0); >>>> + } else { >>>> + /* Caller guarantees that the task is not running. */ >>>> + fp = thread_saved_fp(task); >>>> + pc = thread_saved_pc(task); >>>> + } >>>> + walk_stackframe(task, fp, pc, consume_entry, cookie); >>> >>> I'd prefer to leave this as-is. The new and old structure are largely >>> equivalent, so we haven't made this any simpler, but we have added more >>> arguments to walk_stackframe(). >>> >> >> This is just to simplify things when we eventually add arch_stack_walk_reliable(). >> That is all. All of the unwinding is done by a single unwinding function and >> there are two consumers of that unwinding function - arch_stack_walk() and >> arch_stack_walk_reliable(). > > I understand the theory, but I don't think that moving the start_backtrace() > call actually simplifies this in a meaningful way, and I think it'll make it > harder for us to make more meaningful simplifications later on. > > As of patch 4 of this series, we'll have: > > | noinline notrace void arch_stack_walk(stack_trace_consume_fn consume_entry, > | void *cookie, struct task_struct *task, > | struct pt_regs *regs) > | { > | unsigned long fp, pc; > | > | if (regs) { > | fp = regs->regs[29]; > | pc = regs->pc; > | } else if (task == current) { > | /* Skip arch_stack_walk() in the stack trace. */ > | fp = (unsigned long)__builtin_frame_address(1); > | pc = (unsigned long)__builtin_return_address(0); > | } else { > | /* Caller guarantees that the task is not running. */ > | fp = thread_saved_fp(task); > | pc = thread_saved_pc(task); > | } > | walk_stackframe(task, fp, pc, consume_entry, cookie); > | } > | > | noinline int notrace arch_stack_walk_reliable(stack_trace_consume_fn consume_fn, > | void *cookie, > | struct task_struct *task) > | { > | unsigned long fp, pc; > | > | if (task == current) { > | /* Skip arch_stack_walk_reliable() in the stack trace. */ > | fp = (unsigned long)__builtin_frame_address(1); > | pc = (unsigned long)__builtin_return_address(0); > | } else { > | /* Caller guarantees that the task is not running. */ > | fp = thread_saved_fp(task); > | pc = thread_saved_pc(task); > | } > | if (unwind(task, fp, pc, consume_fn, cookie)) > | return 0; > | return -EINVAL; > | } > > Which I do not think is substantially simpler than the naive extrapolation from > what we currently have, e.g. > > | noinline notrace void arch_stack_walk(stack_trace_consume_fn consume_entry, > | void *cookie, struct task_struct *task, > | struct pt_regs *regs) > | { > | struct stackframe frame; > | > | if (regs) { > | unwind_init(&frame, regs->regs[29], regs->pc) > | } else if (task == current) { > | unwind_init(&frame, __builtin_frame_address(1), > | __builtin_return_address(0)); > | } else { > | unwind_init(&frame, thread_saved_fp(task), > | thread_saved_pc(task); > | } > | walk_stackframe(task, &frame, consume_entry, cookie); > | } > | > | noinline int notrace arch_stack_walk_reliable(stack_trace_consume_fn consume_fn, > | void *cookie, > | struct task_struct *task) > | { > | struct stackframe frame; > | > | if (task == current) { > | unwind_init(&frame, __builtin_frame_address(1), > | __builtin_return_address(0)); > | } else { > | unwind_init(&frame, thread_saved_fp(task), > | thread_saved_pc(task); > | } > | if (unwind(task, &frame, consume_fn, cookie)) > | return 0; > | return -EINVAL; > | } > > Further, I think we can factor this in a different way to reduce the > duplication: > > | /* > | * TODO: document requirements here > | */ > | static inline void unwind_init_from_current_regs(struct stackframe *frame, > | struct pt_regs *regs) > | { > | unwind_init(frame, regs->regs[29], regs->pc); > | } > | > | /* > | * TODO: document requirements here > | */ > | static inline void unwind_init_from_blocked_task(struct stackframe *frame, > | struct task_struct *tsk) > | { > | unwind_init(&frame, thread_saved_fp(task), > | thread_saved_pc(task)); > | } > | > | /* > | * TODO: document requirements here > | * > | * Note: this is always inlined, and we expect our caller to be a noinline > | * function, such that this starts from our caller's caller. > | */ > | static __always_inline void unwind_init_from_caller(struct stackframe *frame) > | { > | unwind_init(frame, __builtin_frame_address(1), > | __builtin_return_address(0)); > | } > | > | noinline notrace void arch_stack_walk(stack_trace_consume_fn consume_entry, > | void *cookie, struct task_struct *task, > | struct pt_regs *regs) > | { > | struct stackframe frame; > | > | if (regs) > | unwind_init_current_regs(&frame, regs); > | else if (task == current) > | unwind_init_from_caller(&frame); > | else > | unwind_init_blocked_task(&frame, task); > | > | unwind(task, &frame, consume_entry, cookie); > | } > | > | noinline int notrace arch_stack_walk_reliable(stack_trace_consume_fn consume_fn, > | void *cookie, > | struct task_struct *task) > | { > | struct stackframe frame; > | > | if (task == current) > | unwind_init_from_caller(&frame); > | else > | unwind_init_from_blocked_task(&frame, task); > | > | if (unwind(task, &frame, consume_fn, cookie)) > | return 0; > | return -EINVAL; > | } > > ... which minimizes the duplication and allows us to add specialized > initialization for each case if necessary, which I believe we will need in > future to make unwinding across exception boundaries (such as when starting > with regs) more useful. > > Thanks, > Mark. > OK. I don't mind doing it this way. Thanks. Madhavan _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel