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=-1.0 required=3.0 tests=MAILING_LIST_MULTI,SPF_PASS 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 7F1C8C43387 for ; Fri, 21 Dec 2018 01:13:53 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 18AFC217D8 for ; Fri, 21 Dec 2018 01:13:52 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 18AFC217D8 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=kernel.crashing.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from lists.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 43LVy56WdRzDr6d for ; Fri, 21 Dec 2018 12:13:49 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=kernel.crashing.org Authentication-Results: lists.ozlabs.org; spf=permerror (mailfrom) smtp.mailfrom=kernel.crashing.org (client-ip=63.228.1.57; helo=gate.crashing.org; envelope-from=benh@kernel.crashing.org; receiver=) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=kernel.crashing.org Received: from gate.crashing.org (gate.crashing.org [63.228.1.57]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 43LVvq1nMtzDr6Q for ; Fri, 21 Dec 2018 12:11:50 +1100 (AEDT) Received: from localhost (localhost.localdomain [127.0.0.1]) by gate.crashing.org (8.14.1/8.14.1) with ESMTP id wBL1BZPN009289; Thu, 20 Dec 2018 19:11:37 -0600 Message-ID: Subject: trace_hardirqs_on/off vs. extra stack frames From: Benjamin Herrenschmidt To: Steven Rostedt Date: Fri, 21 Dec 2018 12:11:35 +1100 Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.30.2 (3.30.2-2.fc29) Mime-Version: 1.0 Content-Transfer-Encoding: 7bit X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linuxppc dev list , Michael Ellerman Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" Hi Steven ! I'm trying to untangle something, and I need your help :-) In commit 3cb5f1a3e58c0bd70d47d9907cc5c65192281dee, you added a summy stack frame around the assembly calls to trace_hardirqs_on/off on the ground that when using the latency tracer (irqsoff), you might poke at CALLER_ADDR1 and that could blow up if there's only one frame at hand. However, I can't see where it would be doing that. lockdep.c only uses CALLER_ADDR0 and irqsoff uses the values passed by it. In fact, that was already the case when the above commit was merged. I tried on a 32-bit kernel to remove the dummy stack frame with no issue so far .... (though I do get stupid values reported with or without a stack frame, but I think that's normal, looking into it). The reason I'm asking is that we have other code path, on return from interrupts for example, at least on 32-bits where we call the tracing without the extra stack frame, and I yet to see it crash. I wonder if the commit and bug fix above relates to some older code that no longer existed even at the point where the commit was merged... Any idea ? Cheers, Ben.