From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754016AbbLJBt2 (ORCPT ); Wed, 9 Dec 2015 20:49:28 -0500 Received: from mail7.hitachi.co.jp ([133.145.228.42]:42255 "EHLO mail7.hitachi.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751720AbbLJBtW (ORCPT ); Wed, 9 Dec 2015 20:49:22 -0500 X-AuditID: 85900ec0-9f5ccb9000001a57-d5-5668da1e79f9 X-Mailbox-Line: From nobody Thu Dec 10 10:46:37 2015 Subject: [V6 PATCH 5/6] x86/nmi: Fix to save registers for crash dump on external NMI broadcast To: Jonathan Corbet , Peter Zijlstra , Ingo Molnar , "Eric W. Biederman" , "H. Peter Anvin" , Andrew Morton , Thomas Gleixner , Vivek Goyal From: Hidehiro Kawai Cc: Baoquan He , linux-doc@vger.kernel.org, x86@kernel.org, kexec@lists.infradead.org, linux-kernel@vger.kernel.org, Steven Rostedt , Michal Hocko , Ingo Molnar , Borislav Petkov , Masami Hiramatsu Date: Thu, 10 Dec 2015 10:46:35 +0900 Message-ID: <20151210014634.25437.217.stgit@softrs> In-Reply-To: <20151210014624.25437.50028.stgit@softrs> References: <20151210014624.25437.50028.stgit@softrs> User-Agent: StGit/0.16 MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit X-Brightmail-Tracker: AAAAAA== Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Now, multiple CPUs can receive external NMI simultaneously by specifying "apic_extnmi=all" as an boot option. When we take a crash dump by using external NMI with this option, we fail to save register values into the crash dump. This happens as follows: CPU 0 CPU 1 ================================ ============================= receive an external NMI default_do_nmi() receive an external NMI spin_lock(&nmi_reason_lock) default_do_nmi() io_check_error() spin_lock(&nmi_reason_lock) panic() busy loop ... kdump_nmi_shootdown_cpus() issue NMI IPI -----------> blocked until IRET busy loop... Here, since CPU 1 is in NMI context, additional NMI from CPU 0 is blocked until CPU 1 executes IRET. However, CPU 1 never executes IRET, so the NMI is not handled and the callback function to save registers is never called. To solve this issue, we check if the IPI for crash dumping was issued while waiting for nmi_reason_lock to be released, and if so, call its callback function directly. If the IPI is not issued (e.g. kdump is disabled), the actual behavior doesn't change. V6: - Separated from the former patch `panic/x86: Allow cpus to save registers even if they are looping in NMI context' - Fix comments - Remove unneeded UP version of poll_crash_ipi_and_calback - Rename poll_crash_ipi_and_callback to run_crash_ipi_callback Signed-off-by: Hidehiro Kawai Cc: Andrew Morton Cc: Thomas Gleixner Cc: Ingo Molnar Cc: "H. Peter Anvin" Cc: Peter Zijlstra Cc: Michal Hocko --- arch/x86/include/asm/reboot.h | 1 + arch/x86/kernel/nmi.c | 11 ++++++++++- arch/x86/kernel/reboot.c | 18 +++++++++++++----- 3 files changed, 24 insertions(+), 6 deletions(-) diff --git a/arch/x86/include/asm/reboot.h b/arch/x86/include/asm/reboot.h index a82c4f1..2cb1cc2 100644 --- a/arch/x86/include/asm/reboot.h +++ b/arch/x86/include/asm/reboot.h @@ -25,5 +25,6 @@ void __noreturn machine_real_restart(unsigned int type); typedef void (*nmi_shootdown_cb)(int, struct pt_regs*); void nmi_shootdown_cpus(nmi_shootdown_cb callback); +void run_crash_ipi_callback(struct pt_regs *regs); #endif /* _ASM_X86_REBOOT_H */ diff --git a/arch/x86/kernel/nmi.c b/arch/x86/kernel/nmi.c index 5e00de7..cbfa0b5 100644 --- a/arch/x86/kernel/nmi.c +++ b/arch/x86/kernel/nmi.c @@ -29,6 +29,7 @@ #include #include #include +#include #define CREATE_TRACE_POINTS #include @@ -357,7 +358,15 @@ static void default_do_nmi(struct pt_regs *regs) } /* Non-CPU-specific NMI: NMI sources can be processed on any CPU */ - raw_spin_lock(&nmi_reason_lock); + /* + * Another CPU may be processing panic routines while holding + * nmi_reason_lock. Check if the CPU issued the IPI for crash + * dumping, and if so, call its callback directly. If there is + * no CPU preparing crash dump, we simply loop here without doing + * special things. + */ + while (!raw_spin_trylock(&nmi_reason_lock)) + run_crash_ipi_callback(regs); reason = x86_platform.get_nmi_reason(); if (reason & NMI_REASON_MASK) { diff --git a/arch/x86/kernel/reboot.c b/arch/x86/kernel/reboot.c index 1da1302..60a216b 100644 --- a/arch/x86/kernel/reboot.c +++ b/arch/x86/kernel/reboot.c @@ -793,17 +793,25 @@ void nmi_shootdown_cpus(nmi_shootdown_cb callback) /* Leave the nmi callback set */ } +/* + * Wait for the crash dumping IPI to be issued, and then call its callback + * directly. This function is used when we have already been in NMI handler. + */ +void run_crash_ipi_callback(struct pt_regs *regs) +{ + if (crash_ipi_issued) + crash_nmi_callback(0, regs); /* Don't return */ +} + /* Override the weak function in kernel/panic.c */ void nmi_panic_self_stop(struct pt_regs *regs) { while (1) { /* - * Wait for the crash dumping IPI to be issued, and then - * call its callback directly. + * If there is no CPU preparing crash dump, we simply loop + * here without doing special things. */ - if (READ_ONCE(crash_ipi_issued)) - crash_nmi_callback(0, regs); /* Don't return */ - + run_crash_ipi_callback(regs); cpu_relax(); } }