From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753537AbdHKREK (ORCPT ); Fri, 11 Aug 2017 13:04:10 -0400 Received: from foss.arm.com ([217.140.101.70]:47478 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752850AbdHKREI (ORCPT ); Fri, 11 Aug 2017 13:04:08 -0400 Message-ID: <598DE33E.6050606@arm.com> Date: Fri, 11 Aug 2017 18:02:54 +0100 From: James Morse User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Icedove/31.6.0 MIME-Version: 1.0 To: Hoeun Ryu CC: Catalin Marinas , Will Deacon , Mark Rutland , AKASHI Takahiro , Robin Murphy , Ard Biesheuvel , Ingo Molnar , "Peter Zijlstra (Intel)" , Suzuki K Poulose , David Daney , Rob Herring , Kefeng Wang , Thomas Gleixner , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCHv2] arm64:kexec: have own crash_smp_send_stop() for crash dump for nonpanic cores References: <1502082623-23952-1-git-send-email-hoeun.ryu@gmail.com> In-Reply-To: <1502082623-23952-1-git-send-email-hoeun.ryu@gmail.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Hoeun, On 07/08/17 06:09, Hoeun Ryu wrote: > Commit 0ee5941 : (x86/panic: replace smp_send_stop() with kdump friendly > version in panic path) introduced crash_smp_send_stop() which is a weak > function and can be overriden by architecture codes to fix the side effect (overridden) > caused by commit f06e515 : (kernel/panic.c: add "crash_kexec_post_ > notifiers" option). > > ARM64 architecture uses the weak version function and the problem is that > the weak function simply calls smp_send_stop() which makes other CPUs > offline and takes away the chance to save crash information for nonpanic > CPUs in machine_crash_shutdown() when crash_kexec_post_notifiers kernel > option is enabled. > > Calling smp_send_crash_stop() in machine_crash_shutdown() is useless > because all nonpanic CPUs are already offline by smp_send_stop() in this > case and smp_send_crash_stop() only works against online CPUs. > The result is that /proc/vmcore is not available with the error messages; > "Warning: Zero PT_NOTE entries found", "Kdump: vmcore not initialized". When I tried this I got one of these warnings for each secondary CPU, but the vmcore file was still available. When I ran 'crash' on the vmcore it reported: > CPUS: 6 [OFFLINE: 5] Did I miss as step to reproduce this? If not, can we change this paragraph to say something like: > The result is that secondary CPUs registers are not saved by crash_save_cpu() > and the vmcore file misreports these CPUs as being offline. > crash_smp_send_stop() is implemented to fix this problem by replacing the > exising smp_send_crash_stop() and adding a check for multiple calling to (existing) > the function. The function (strong symbol version) saves crash information > for nonpanic CPUs and machine_crash_shutdown() tries to save crash > information for nonpanic CPUs only when crash_kexec_post_notifiers kernel > option is disabled. > > * crash_kexec_post_notifiers : false > > panic() > __crash_kexec() > machine_crash_shutdown() > crash_smp_send_stop() <= save crash dump for nonpanic cores > > * crash_kexec_post_notifiers : true > > panic() > crash_smp_send_stop() <= save crash dump for nonpanic cores > __crash_kexec() > machine_crash_shutdown() > crash_smp_send_stop() <= just return. > diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c > index dc66e6e..73d8f5e 100644 > --- a/arch/arm64/kernel/smp.c > +++ b/arch/arm64/kernel/smp.c > @@ -977,11 +977,21 @@ void smp_send_stop(void) > } > > #ifdef CONFIG_KEXEC_CORE > -void smp_send_crash_stop(void) > +void crash_smp_send_stop(void) > { > + static int cpus_stopped; > cpumask_t mask; > unsigned long timeout; > > + /* > + * This function can be called twice in panic path, but obviously > + * we execute this only once. > + */ > + if (cpus_stopped) > + return; > + > + cpus_stopped = 1; > + This cpus_stopped=1 can't happen on multiple CPUs at the same time as any second call is guaranteed to be on the same CPU, both are behind panic()s 'atomic_cmpxchg()'. Other than my '/proc/vmcore is not available' question above, this looks fine to me: Reviewed-by: James Morse Tested-by: James Morse Thanks! James