Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752496AbbLKSEJ (ORCPT ); Fri, 11 Dec 2015 13:04:09 -0500 Received: from mail.skyhub.de ([78.46.96.112]:53638 "EHLO mail.skyhub.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751918AbbLKSEH (ORCPT ); Fri, 11 Dec 2015 13:04:07 -0500 Date: Fri, 11 Dec 2015 19:04:03 +0100 From: Borislav Petkov To: Hidehiro Kawai Cc: Jonathan Corbet , Peter Zijlstra , Ingo Molnar , "Eric W. Biederman" , "H. Peter Anvin" , Andrew Morton , Thomas Gleixner , Vivek Goyal , 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 , Masami Hiramatsu Subject: Re: [V6.1 PATCH 5/6] x86/nmi: Fix to save registers for crash dump on external NMI broadcast Message-ID: <20151211180403.GD4815@pd.tnic> References: <20151210014634.25437.217.stgit@softrs> <201512101102.6UNkKzbX%fengguang.wu@intel.com> <04EAB7311EE43145B2D3536183D1A84454A4EA10@GSjpTKYDCembx31.service.hitachi.net> <20151210065245.4587.39316.stgit@softrs> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20151210065245.4587.39316.stgit@softrs> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4238 Lines: 107 On Thu, Dec 10, 2015 at 03:52:46PM +0900, Hidehiro Kawai wrote: > 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. > > V6.1: > - Reintroduce the UP version of run_crash_ipi_callback to fix build > error for CONFIG_SMP=n and CONFIG_DEBUG_SPINLOCK=y case > > 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 | 22 +++++++++++++++++----- > 3 files changed, 28 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); Added cpu_relax() here too: + while (!raw_spin_trylock(&nmi_reason_lock)) { + run_crash_ipi_callback(regs); + cpu_relax(); + } -- Regards/Gruss, Boris. ECO tip #101: Trim your mails when you reply. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/