From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from gate.crashing.org (gate.crashing.org [63.228.1.57]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client did not present a certificate) by ozlabs.org (Postfix) with ESMTPS id AC912B7D72 for ; Tue, 25 May 2010 05:23:43 +1000 (EST) Subject: Re: [PATCH 2/2] powerpc, kdump: Fix race in kdump shutdown Mime-Version: 1.0 (Apple Message framework v1078) Content-Type: text/plain; charset=us-ascii From: Kumar Gala In-Reply-To: <20100514054011.5E585D34AB@localhost.localdomain> Date: Mon, 24 May 2010 14:23:27 -0500 Message-Id: References: <20100514054011.5E585D34AB@localhost.localdomain> To: Michael Neuling Cc: jlarrew@linux.vnet.ibm.com, kexec@lists.infradead.org, Anton Blanchard , linuxppc-dev@ozlabs.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 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. >=20 > 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. >=20 > We've hit this on large POWER7 machines, where some secondaries are > still waiting in lock_rtas(), when the primary tears down the HPTEs. >=20 > 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. >=20 > Signed-off-by: Michael Neuling > --- >=20 > arch/powerpc/kernel/crash.c | 27 +++++++++++++++++++++++++++ > 1 file changed, 27 insertions(+) >=20 > Index: linux-2.6-ozlabs/arch/powerpc/kernel/crash.c > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D > --- 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 */ > } >=20 > +/* 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 =3D 10000; > + for (i=3D0; i < NR_CPUS && msecs > 0; i++) { > + if (i =3D=3D 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 - k