From patchwork Wed Jan 21 10:47:37 2015 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Daniel Thompson X-Patchwork-Id: 5676291 Return-Path: X-Original-To: patchwork-linux-arm@patchwork.kernel.org Delivered-To: patchwork-parsemail@patchwork2.web.kernel.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.136]) by patchwork2.web.kernel.org (Postfix) with ESMTP id AD4EBC058D for ; Wed, 21 Jan 2015 10:49:46 +0000 (UTC) Received: from mail.kernel.org (localhost [127.0.0.1]) by mail.kernel.org (Postfix) with ESMTP id C7C2F2050B for ; Wed, 21 Jan 2015 10:49:45 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.9]) (using TLSv1.2 with cipher DHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 000FC2018E for ; Wed, 21 Jan 2015 10:49:44 +0000 (UTC) Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.80.1 #2 (Red Hat Linux)) id 1YDspN-0004mw-V7; Wed, 21 Jan 2015 10:48:01 +0000 Received: from mail-we0-f169.google.com ([74.125.82.169]) by bombadil.infradead.org with esmtps (Exim 4.80.1 #2 (Red Hat Linux)) id 1YDspJ-0004e6-QZ for linux-arm-kernel@lists.infradead.org; Wed, 21 Jan 2015 10:47:58 +0000 Received: by mail-we0-f169.google.com with SMTP id p10so18867642wes.0 for ; Wed, 21 Jan 2015 02:47:35 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:message-id:date:from:user-agent:mime-version:to :cc:subject:references:in-reply-to:content-type :content-transfer-encoding; bh=1lOYFiIFwHeGpi71UB0kdLso7iqQGnCEQ2tAFu/v6Ho=; b=LdLyUluVl96i/oT/rnstXIYf0sPrlK/XWoqHe8ZFpzjlMxInJJuRUlUjyK2u0l1aYb ndMPlKrnZprgojpBkoQnKMtPUG9RyYYI7ybSbaaRL7RuCioB5EDfRMrAgErGT7ZN4KPn GRdNh327ZEuWf9KPv9HSuT66ew03B5pAUc42L6DsCmG3EmUc5om6k9RnMNwfWcNv9vwL /Z1G9JqRvfbEgGE9I+Phb53PKncv9eGVmzAuKJxoPvJtOttXL0AAXaqNoNHlZ2y+Fi/N QKqUCSXCdzyDp7bt4TDrPIC8BACMuAEKzTKI/uXzhL/obQT2BCXeaUnUQ6wHBpOpM60h MWaw== X-Gm-Message-State: ALoCoQmEbHm2SeEWH8mBPdmDlFM1KP9HdCyBDwYlaD7T+5aflGJLjWAEaXQYu9FF2MmBslPBEuuO X-Received: by 10.194.80.193 with SMTP id t1mr60863290wjx.8.1421837255246; Wed, 21 Jan 2015 02:47:35 -0800 (PST) Received: from harvey.bri.st.com (cpc4-aztw19-0-0-cust157.18-1.cable.virginm.net. [82.33.25.158]) by mx.google.com with ESMTPSA id be2sm24963393wjb.38.2015.01.21.02.47.33 (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 21 Jan 2015 02:47:34 -0800 (PST) Message-ID: <54BF83C9.5060300@linaro.org> Date: Wed, 21 Jan 2015 10:47:37 +0000 From: Daniel Thompson User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.3.0 MIME-Version: 1.0 To: Stephen Boyd , Thomas Gleixner , Jason Cooper Subject: Re: [PATCH 3.19-rc2 v14 0/7] arm: Implement arch_trigger_all_cpu_backtrace References: <1415968543-29469-1-git-send-email-daniel.thompson@linaro.org> <1421144818-14036-1-git-send-email-daniel.thompson@linaro.org> <54BE2D15.9080606@linaro.org> <54BEC04D.1050402@codeaurora.org> In-Reply-To: <54BEC04D.1050402@codeaurora.org> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20150121_024758_016782_63FB015F X-CRM114-Status: GOOD ( 16.66 ) X-Spam-Score: -0.7 (/) Cc: linaro-kernel@lists.linaro.org, Russell King , patches@linaro.org, linux-kernel@vger.kernel.org, Steven Rostedt , Daniel Drake , Dmitry Pervushin , Dirk Behme , John Stultz , Tim Sander , Sumit Semwal , linux-arm-kernel@lists.infradead.org X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.18-1 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+patchwork-linux-arm=patchwork.kernel.org@lists.infradead.org X-Spam-Status: No, score=-4.2 required=5.0 tests=BAYES_00, RCVD_IN_DNSWL_MED, T_RP_MATCHES_RCVD, UNPARSEABLE_RELAY autolearn=unavailable version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on mail.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP On 20/01/15 20:53, Stephen Boyd wrote: > On 01/20/2015 02:25 AM, Daniel Thompson wrote: >> On 13/01/15 10:26, Daniel Thompson wrote: >>> Hi Thomas, Hi Jason: >>> Patches 1 to 3 are for you (and should be separable from the rest >>> of the series). The patches haven't changes since the last time >>> I posted them. The changes in v14 tidy up the later part of the >>> patch set in order to share more code between x86 and arm. >> No review comments! Have I finally got this right? >> >> If so it possible and/or sensible to get patches 1-3 in a tree that >> feeds linux-next. I'd really like the gic changes to meet the various >> ARM build and boot bots. > > With this patchset, is it possible to call sched_clock() from within NMI > context? I ask because the generic sched_clock() code is not NMI safe > today. We were planning on making it NMI safe by doing something similar > to what was done for ktime_get_mono_fast_ns() but we haven't gotten > around to it. Mostly because no architecture that uses generic > sched_clock() has support for NMIs right now. I've not done any work to make sched_clock() safe to call from NMI. However since my patchset does not introduce any calls to sched_clock() from NMI I think this is OK! I ported Steven Rostedt's work to make arch_trigger_all_cpu_backtrace() safe from NMI from x86 to ARM. One result of Steven's approach are that printk() timestamping is deferred until we return to normal context. Thus even with CONFIG_PRINTK_TIME we do not call local_clock() during NMI processing. To confirm the above I have added the code below to my kernel and ran it with a fairly paranoid set of debugging options. The check does not fire. Daniel. diff --git a/include/asm-generic/bug.h b/include/asm-generic/bug.h index 630dd2372238..fea0deeb524b 100644 --- a/include/asm-generic/bug.h +++ b/include/asm-generic/bug.h @@ -111,8 +111,10 @@ extern void warn_slowpath_null(const char *file, const int line); int __ret_warn_once = !!(condition); \ \ if (unlikely(__ret_warn_once)) \ - if (WARN_ON(!__warned)) \ + if (unlikely(!__warned)) { \ __warned = true; \ + __WARN(); \ + } \ unlikely(__ret_warn_once); \ }) diff --git a/kernel/time/sched_clock.c b/kernel/time/sched_clock.c index 01d2d15aa662..81ea469b7e68 100644 --- a/kernel/time/sched_clock.c +++ b/kernel/time/sched_clock.c @@ -63,6 +63,8 @@ unsigned long long notrace sched_clock(void) u64 cyc; unsigned long seq; + WARN_ON_ONCE(in_nmi()); + if (cd.suspended) return cd.epoch_ns;