From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757252Ab1CSSOo (ORCPT ); Sat, 19 Mar 2011 14:14:44 -0400 Received: from e23smtp05.au.ibm.com ([202.81.31.147]:60975 "EHLO e23smtp05.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757117Ab1CSSOk (ORCPT ); Sat, 19 Mar 2011 14:14:40 -0400 Date: Sat, 19 Mar 2011 23:44:33 +0530 From: Kamalesh Babulal To: greg@kroah.com Cc: stable@kernel.org, linux-kernel@vger.kernel.org, anton@samba.org, benh@kernel.crashing.org, mananth@in.ibm.com Subject: [2/3] powerpc/kdump: Fix race in kdump shutdown Message-ID: <20110319181433.GC23832@linux.vnet.ibm.com> Reply-To: Kamalesh Babulal MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org powerpc/kdump: Fix race in kdump shutdown Commit: 60adec6226bbcf061d4c2d10944fced209d1847d upstream When we are crashing, the crashing/primary CPU IPIs the secondaries to turn off IRQs, go into real mode and wait in kexec_wait. While this is happening, the primary tears down all the MMU maps. Unfortunately the primary doesn't check to make sure the secondaries have entered real mode before doing this. On PHYP machines, the secondaries can take a long time shutting down the IRQ controller as RTAS calls are need. These RTAS calls need to be serialised which resilts in the secondaries contending in lock_rtas() and hence taking a long time to shut down. We've hit this on large POWER7 machines, where some secondaries are still waiting in lock_rtas(), when the primary tears down the HPTEs. This patch makes sure all secondaries are in real mode before the primary tears down the MMU. It uses the new kexec_state entry in the paca. It times out if the secondaries don't reach real mode after 10sec. Signed-off-by: Michael Neuling Signed-off-by: Benjamin Herrenschmidt Signed-off-by: Kamalesh Babulal cc: Anton Blanchard --- arch/powerpc/kernel/crash.c | 28 ++++++++++++++++++++++++++++ 1 files changed, 28 insertions(+), 0 deletions(-) diff --git a/arch/powerpc/kernel/crash.c b/arch/powerpc/kernel/crash.c index b779818..706b622 100644 --- a/arch/powerpc/kernel/crash.c +++ b/arch/powerpc/kernel/crash.c @@ -153,6 +153,7 @@ static void crash_kexec_prepare_cpus(int cpu) while (cpus_weight(cpus_in_crash) < ncpus) cpu_relax(); } + /* * Make sure all CPUs are entered via soft-reset if the kdump is * invoked using soft-reset. @@ -162,6 +163,32 @@ static void crash_kexec_prepare_cpus(int cpu) /* Leave the IPI callback set */ } +/* wait for all the CPUs to hit real mode but timeout if they don't come in */ +static void crash_kexec_wait_realmode(int cpu) +{ + unsigned int msecs; + int i; + + msecs = 10000; + for (i = 0; i < NR_CPUS && msecs > 0; i++) { + if (i == cpu) + continue; + + while (paca[i].kexec_state < KEXEC_STATE_REAL_MODE) { + barrier(); + if (!cpu_possible(i)) + break; + + if (!cpu_online(i)) + break; + + msecs--; + mdelay(1); + } + } + mb(); +} + /* * This function will be called by secondary cpus or by kexec cpu * if soft-reset is activated to stop some CPUs. @@ -419,6 +446,7 @@ void default_machine_crash_shutdown(struct pt_regs *regs) crash_kexec_prepare_cpus(crashing_cpu); cpu_set(crashing_cpu, cpus_in_crash); crash_kexec_stop_spus(); + crash_kexec_wait_realmode(crashing_cpu); if (ppc_md.kexec_cpu_down) ppc_md.kexec_cpu_down(1, 0); }