Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752608AbaJPMXh (ORCPT ); Thu, 16 Oct 2014 08:23:37 -0400 Received: from gw-1.arm.linux.org.uk ([78.32.30.217]:35683 "EHLO pandora.arm.linux.org.uk" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752583AbaJPMXg (ORCPT ); Thu, 16 Oct 2014 08:23:36 -0400 Date: Thu, 16 Oct 2014 13:23:23 +0100 From: Russell King - ARM Linux To: Daniel Thompson Cc: Daniel Drake , linaro-kernel@lists.linaro.org, patches@linaro.org, Linux Kernel , John Stultz , Thomas Gleixner , Sumit Semwal , "linux-arm-kernel@lists.infradead.org" Subject: Re: [PATCH 3.17-rc4 v7 0/6] arm: Implement arch_trigger_all_cpu_backtrace Message-ID: <20141016122322.GO27405@n2100.arm.linux.org.uk> References: <1410970218-28847-1-git-send-email-daniel.thompson@linaro.org> <543F8EA8.6080905@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <543F8EA8.6080905@linaro.org> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Oct 16, 2014 at 10:23:52AM +0100, Daniel Thompson wrote: > On 14/10/14 23:37, Daniel Drake wrote: > > I'm testing your patches on Exynos4412 and I guess in their current > > state they don't go quite this deep, as the only callers of > > trigger_all_cpu_backtrace() are sysrq, hung_task and spinlock debug > > code - none of which seem as fail-safe as a trigger like a > > pre-programmed watchdog NMI interrupt would be. > > > > Do I need to find a way to get CONFIG_FIQ available on this platform > > first? and/or CONFIG_HARDLOCKUP_DETECTOR? > > You need CONFIG_FIQ working first. Be aware that this may be impossible > on Exynos unless you control the TrustZone. For this reason most of my > development is on Freescale i.MX6 (because i.MX6 boots in secure mode). CONFIG_FIQ enables the legacy FIQ code which is unsuitable for use on SMP, so that should not be a requirement. We still need to validate all the code we're proposing to run in FIQ context does not violate any locking. IRQ-safe locks will do not prevent FIQs occuring, and using IRQ-safe locks which are also taken in the FIQ path /will/ cause deadlocks. So, we need to ensure that the perf internals are safe for this. Lastly, platforms running in non-secure mode most likely will not be able to take /any/ advantage from the FIQ stuff because FIQs will likely only be available to the secure firmware. -- FTTC broadband for 0.8mile line: currently at 9.5Mbps down 400kbps up according to speedtest.net. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/