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 7CCD0C43387 for ; Fri, 21 Dec 2018 02:05:30 +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 B6F45218E0 for ; Fri, 21 Dec 2018 02:05:29 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B6F45218E0 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=goodmis.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 43LX5g3Mm2zDr2N for ; Fri, 21 Dec 2018 13:05:27 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=goodmis.org Authentication-Results: lists.ozlabs.org; spf=pass (mailfrom) smtp.mailfrom=kernel.org (client-ip=198.145.29.99; helo=mail.kernel.org; envelope-from=srs0=8qkb=o6=goodmis.org=rostedt@kernel.org; receiver=) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=goodmis.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 43LX2t1qjQzDqwh for ; Fri, 21 Dec 2018 13:03:02 +1100 (AEDT) Received: from vmware.local.home (cpe-66-24-56-78.stny.res.rr.com [66.24.56.78]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id D7BC8218E0; Fri, 21 Dec 2018 02:02:59 +0000 (UTC) Date: Thu, 20 Dec 2018 21:02:57 -0500 From: Steven Rostedt To: Benjamin Herrenschmidt Subject: Re: trace_hardirqs_on/off vs. extra stack frames Message-ID: <20181220210257.743426dd@vmware.local.home> In-Reply-To: References: X-Mailer: Claws Mail 3.15.1 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII 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" On Fri, 21 Dec 2018 12:11:35 +1100 Benjamin Herrenschmidt wrote: > 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). BTW, I only had a 64 bit PPC working, so I would have been testing that. > > 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. Have you tried enabling the irqsoff tracer and running it for a while? echo irqsoff > /sys/kernel/debug/tracing/current_tracer The problem is that when we come from user space, and we disable interrupts in the entry code, it calls into the irqsoff tracer: [ in userspace ] [ in kernel ] bl .trace_hardirqs_off kernel/trace/trace_preemptirq.c: trace_hardirqs_off(CALLER_ADDR_0, CALLER_ADDR1) IIRC, without the stack frame, that CALLER_ADDR1 can end up having the kernel read garbage. -- Steve > > 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... >