From patchwork Mon Nov 29 14:28:45 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Mark Rutland X-Patchwork-Id: 12693915 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 0057EC433F5 for ; Mon, 29 Nov 2021 14:32:09 +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:MIME-Version:References:In-Reply-To: Message-Id:Date:Subject:Cc:To:From:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=oxPPJYPabJqC1DxY5N+khWTW3Q7PyU4LDds5RnDQokQ=; b=BN8rffYxrk8IDT Bf6B1aVqkvCu1iYB7isP1EvpQ4Rdv1KpyH78bnqHd2wyh9bLIXDO6cUW6hIwJXYAzRrpYOocziy65 fdqyWPpbNWtNwJ+HambMLG48+Obvd5tZLpIkP0X2sHXsqLIyZ+iP5IjVWRkmRic8yoB1QrqKXmzv9 SK6aAbOLPzdV19IcT9lV4yb5DEkMgw7TeMAJeXxIDQ/tlHb/h/umDuO17iVasWdRaaLsCZ5tOXi43 0SDNroYfAS+X0fMgpjm+tlKNXjvnTAW2VhpvUz+Jh5B09fqxtSAbuX3P60EsGtzpBpjvJx1K+/CD4 cB97oURWWZ/9TUq+5yRQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1mrhfh-0012pP-Ml; Mon, 29 Nov 2021 14:30:21 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1mrhee-0012MF-JZ for linux-arm-kernel@lists.infradead.org; Mon, 29 Nov 2021 14:29:19 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 4CB7913A1; Mon, 29 Nov 2021 06:29:15 -0800 (PST) Received: from lakrids.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id C49463F766; Mon, 29 Nov 2021 06:29:12 -0800 (PST) From: Mark Rutland To: linux-arm-kernel@lists.infradead.org Cc: aou@eecs.berkeley.edu, borntraeger@de.ibm.com, bp@alien8.de, broonie@kernel.org, catalin.marinas@arm.com, dave.hansen@linux.intel.com, gor@linux.ibm.com, hca@linux.ibm.com, madvenka@linux.microsoft.com, mark.rutland@arm.com, mhiramat@kernel.org, mingo@redhat.com, mpe@ellerman.id.au, palmer@dabbelt.com, paul.walmsley@sifive.com, peterz@infradead.org, rostedt@goodmis.org, tglx@linutronix.de, will@kernel.org Subject: [PATCH v2 5/9] arm64: Make __get_wchan() use arch_stack_walk() Date: Mon, 29 Nov 2021 14:28:45 +0000 Message-Id: <20211129142849.3056714-6-mark.rutland@arm.com> X-Mailer: git-send-email 2.30.2 In-Reply-To: <20211129142849.3056714-1-mark.rutland@arm.com> References: <20211129142849.3056714-1-mark.rutland@arm.com> MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20211129_062916_755638_C4CD98EB X-CRM114-Status: GOOD ( 16.53 ) 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: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org From: "Madhavan T. Venkataraman" To enable RELIABLE_STACKTRACE and LIVEPATCH on arm64, we need to substantially rework arm64's unwinding code. As part of this, we want to minimize the set of unwind interfaces we expose, and avoid open-coding of unwind logic outside of stacktrace.c. Currently, __get_wchan() walks the stack of a blocked task by calling start_backtrace() with the task's saved PC and FP values, and iterating unwind steps using unwind_frame(). The initialization is functionally equivalent to calling arch_stack_walk() with the blocked task, which will start with the task's saved PC and FP values. Currently __get_wchan() always performs an initial unwind step, which will stkip __switch_to(), but as this is now marked as a __sched function, this no longer needs special handling and will be skipped in the same way as other sched functions. Make __get_wchan() use arch_stack_walk(). This simplifies __get_wchan(), and in future will alow us to make unwind_frame() private to stacktrace.c. At the same time, we can simplify the try_get_task_stack() check and avoid the unnecessary `stack_page` variable. The change to the skipping logic means we may terminate one frame earlier than previously where there are an excessive number of sched functions in the trace, but this isn't seen in practice, and wchan is best-effort anyway, so this should not be a problem. Other than the above, there should be no functional change as a result of this patch. Signed-off-by: Madhavan T. Venkataraman [Mark: rebase atop wchan changes, elaborate commit message, fix includes] Signed-off-by: Mark Rutland Reviewed-by: Mark Brown --- arch/arm64/kernel/process.c | 42 ++++++++++++++++++++++--------------- 1 file changed, 25 insertions(+), 17 deletions(-) diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c index 980cad7292af..836a933156cd 100644 --- a/arch/arm64/kernel/process.c +++ b/arch/arm64/kernel/process.c @@ -40,6 +40,7 @@ #include #include #include +#include #include #include @@ -529,30 +530,37 @@ struct task_struct *__switch_to(struct task_struct *prev, return last; } +struct wchan_info { + unsigned long pc; + int count; +}; + +static bool get_wchan_cb(void *arg, unsigned long pc) +{ + struct wchan_info *wchan_info = arg; + + if (!in_sched_functions(pc)) { + wchan_info->pc = pc; + return false; + } + return wchan_info->count++ < 16; +} + unsigned long __get_wchan(struct task_struct *p) { - struct stackframe frame; - unsigned long stack_page, ret = 0; - int count = 0; + struct wchan_info wchan_info = { + .pc = 0, + .count = 0, + }; - stack_page = (unsigned long)try_get_task_stack(p); - if (!stack_page) + if (!try_get_task_stack(p)) return 0; - start_backtrace(&frame, thread_saved_fp(p), thread_saved_pc(p)); - - do { - if (unwind_frame(p, &frame)) - goto out; - if (!in_sched_functions(frame.pc)) { - ret = frame.pc; - goto out; - } - } while (count++ < 16); + arch_stack_walk(get_wchan_cb, &wchan_info, p, NULL); -out: put_task_stack(p); - return ret; + + return wchan_info.pc; } unsigned long arch_align_stack(unsigned long sp)