Commits
Hidehiro Kawai committed b279d67df88
x86/nmi: Save regs in crash dump on external NMI Now, multiple CPUs can receive an external NMI simultaneously by specifying the "apic_extnmi=all" command line parameter. When we take a crash dump by using external NMI with this option, we fail to save registers 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, an additional NMI from CPU 0 remains unhandled until CPU 1 IRETs. However, CPU 1 will never execute 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. Signed-off-by: Hidehiro Kawai <hidehiro.kawai.ez@hitachi.com> Acked-by: Michal Hocko <mhocko@suse.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Andy Lutomirski <luto@kernel.org> Cc: Baoquan He <bhe@redhat.com> Cc: Dave Young <dyoung@redhat.com> Cc: "Eric W. Biederman" <ebiederm@xmission.com> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: Ingo Molnar <mingo@kernel.org> Cc: Jiang Liu <jiang.liu@linux.intel.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: kexec@lists.infradead.org Cc: linux-doc@vger.kernel.org Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Stefan Lippers-Hollmann <s.l-h@gmx.de> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Vivek Goyal <vgoyal@redhat.com> Cc: x86-ml <x86@kernel.org> Link: http://lkml.kernel.org/r/20151210065245.4587.39316.stgit@softrs Signed-off-by: Borislav Petkov <bp@suse.de> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>