From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752536AbbIOLaZ (ORCPT ); Tue, 15 Sep 2015 07:30:25 -0400 Received: from pandora.arm.linux.org.uk ([78.32.30.218]:50032 "EHLO pandora.arm.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752465AbbIOLaV (ORCPT ); Tue, 15 Sep 2015 07:30:21 -0400 Date: Tue, 15 Sep 2015 12:30:03 +0100 From: Russell King - ARM Linux To: Daniel Thompson Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, patches@linaro.org, linaro-kernel@lists.linaro.org, Thomas Gleixner , Hillf Danton Subject: Re: [PATCH v2] arm: Fix backtrace generation when IPI is masked Message-ID: <20150915113003.GS21084@n2100.arm.linux.org.uk> References: <1442222294-2756-1-git-send-email-daniel.thompson@linaro.org> <1442315112-14039-1-git-send-email-daniel.thompson@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1442315112-14039-1-git-send-email-daniel.thompson@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 Tue, Sep 15, 2015 at 12:05:12PM +0100, Daniel Thompson wrote: > Currently on ARM when is triggered from an interrupt handler > (e.g. a SysRq issued using UART or kbd) the main CPU will wedge for ten > seconds with interrupts masked before issuing a backtrace for every CPU > except itself. > > The new backtrace code introduced by commit 96f0e00378d4 ("ARM: add > basic support for on-demand backtrace of other CPUs") does not work > correctly when run from an interrupt handler because IPI_CPU_BACKTRACE > is used to generate the backtrace on all CPUs but cannot preempt the > current calling context. This patch needs a little more work - what happens to the IPI_CPU_BACKTRACE we've sent to ourselves? (It fires after the interrupt handler for the UART/kbd has finished.) It ought to be masked out if we're going to handle it a different way. -- FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up according to speedtest.net.