From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from gate.crashing.org ([63.228.1.57]) by bombadil.infradead.org with esmtps (Exim 4.69 #1 (Red Hat Linux)) id 1OGdL8-000361-8v for kexec@lists.infradead.org; Mon, 24 May 2010 19:29:31 +0000 Subject: Re: [PATCH 2/2] powerpc, kdump: Fix race in kdump shutdown Mime-Version: 1.0 (Apple Message framework v1078) From: Kumar Gala In-Reply-To: Date: Mon, 24 May 2010 14:29:24 -0500 Message-Id: <04AC722A-97CD-4451-B6AB-F4AC37EFAB1D@kernel.crashing.org> References: <20100514054011.5E585D34AB@localhost.localdomain> List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: kexec-bounces@lists.infradead.org Errors-To: kexec-bounces+dwmw2=infradead.org@lists.infradead.org To: Kumar Gala Cc: linuxppc-dev@ozlabs.org, Michael Neuling , kexec@lists.infradead.org, jlarrew@linux.vnet.ibm.com, Anton Blanchard On May 24, 2010, at 2:23 PM, Kumar Gala wrote: > > On May 14, 2010, at 12:40 AM, Michael Neuling wrote: > >> 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 >> --- >> >> arch/powerpc/kernel/crash.c | 27 +++++++++++++++++++++++++++ >> 1 file changed, 27 insertions(+) >> >> Index: linux-2.6-ozlabs/arch/powerpc/kernel/crash.c >> =================================================================== >> --- linux-2.6-ozlabs.orig/arch/powerpc/kernel/crash.c >> +++ linux-2.6-ozlabs/arch/powerpc/kernel/crash.c >> @@ -162,6 +162,32 @@ static void crash_kexec_prepare_cpus(int >> /* 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. >> @@ -412,6 +438,7 @@ void default_machine_crash_shutdown(stru >> crash_kexec_prepare_cpus(crashing_cpu); >> cpu_set(crashing_cpu, cpus_in_crash); >> crash_kexec_stop_spus(); > > should this be > > #ifdef CONFIG_PPC_STD_MMU > >> + crash_kexec_wait_realmode(crashing_cpu); > > #endif I'm going to make it CONFIG_PPC_STD_MMU_64 as part of a Kexec book-e patch - k _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec