Ping Boris On 02/23/2017 at 09:36 PM, Xunlei Pang wrote: > We met an issue for kdump: after kdump kernel boots up, > and there comes a broadcasted mce in first kernel, the > other cpus remaining in first kernel will enter the old > mce handler of first kernel, then timeout and panic due > to MCE synchronization, finally reset the kdump cpus. > > This patch lets cpus stay quiet after nmi_shootdown_cpus(), > so after kdump boots, cpus remaining in 1st kernel should > not do anything except clearing MCG_STATUS. This is useful > for kdump to let vmcore dumping perform as hard as it can. > > Previous efforts: > https://patchwork.kernel.org/patch/6167631/ > https://lists.gt.net/linux/kernel/2146557 > > Cc: Naoya Horiguchi <n-horiguchi at ah.jp.nec.com> > Suggested-by: Borislav Petkov <bp at alien8.de> > Signed-off-by: Xunlei Pang <xlpang at redhat.com> > --- > v1->v2: > - Using crashing_cpu according to Borislav's suggestion. > > v2->v3: > - Used crashing_cpu in mce.c explicitly, not skip crashing_cpu. > - Added some comments. > > v3->v4: > - Added more code comments according to Tony's feedback. > > arch/x86/include/asm/reboot.h | 1 + > arch/x86/kernel/cpu/mcheck/mce.c | 17 +++++++++++++++-- > arch/x86/kernel/reboot.c | 5 +++-- > 3 files changed, 19 insertions(+), 4 deletions(-) > > diff --git a/arch/x86/include/asm/reboot.h b/arch/x86/include/asm/reboot.h > index 2cb1cc2..fc62ba8 100644 > --- a/arch/x86/include/asm/reboot.h > +++ b/arch/x86/include/asm/reboot.h > @@ -15,6 +15,7 @@ struct machine_ops { > }; > > extern struct machine_ops machine_ops; > +extern int crashing_cpu; > > void native_machine_crash_shutdown(struct pt_regs *regs); > void native_machine_shutdown(void); > diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c > index 8e9725c..b65505f 100644 > --- a/arch/x86/kernel/cpu/mcheck/mce.c > +++ b/arch/x86/kernel/cpu/mcheck/mce.c > @@ -49,6 +49,7 @@ > #include <asm/tlbflush.h> > #include <asm/mce.h> > #include <asm/msr.h> > +#include <asm/reboot.h> > > #include "mce-internal.h" > > @@ -1127,9 +1128,21 @@ void do_machine_check(struct pt_regs *regs, long error_code) > * on Intel. > */ > int lmce = 1; > + int cpu = smp_processor_id(); > > - /* If this CPU is offline, just bail out. */ > - if (cpu_is_offline(smp_processor_id())) { > + /* > + * Cases to bail out to avoid rendezvous process timeout: > + * 1)If this CPU is offline. > + * 2)If crashing_cpu was set, e.g. entering kdump, > + * we need to skip cpus remaining in 1st kernel. > + * Note: there is a small window between kexecing > + * and kdump kernel establishing new mce handler, > + * if some MCE comes within the window, there is > + * no valid mce handler due to pgtable changing, > + * let's just face the fate. > + */ > + if (cpu_is_offline(cpu) || > + (crashing_cpu != -1 && crashing_cpu != cpu)) { > u64 mcgstatus; > > mcgstatus = mce_rdmsrl(MSR_IA32_MCG_STATUS); > diff --git a/arch/x86/kernel/reboot.c b/arch/x86/kernel/reboot.c > index e244c19..92ecf4b 100644 > --- a/arch/x86/kernel/reboot.c > +++ b/arch/x86/kernel/reboot.c > @@ -749,10 +749,11 @@ void machine_crash_shutdown(struct pt_regs *regs) > #endif > > > +/* This keeps a track of which one is crashing cpu. */ > +int crashing_cpu = -1; > + > #if defined(CONFIG_SMP) > > -/* This keeps a track of which one is crashing cpu. */ > -static int crashing_cpu; > static nmi_shootdown_cb shootdown_callback; > > static atomic_t waiting_for_crash_ipi;
