On Fri, Jul 26, 2013 at 10:38 PM, Stephen Warren <swarren at wwwdotorg.org> wrote: > On 07/26/2013 04:49 AM, Will Deacon wrote: >> [Adding Stephen Warren since he has been working in this area] >> >> On Fri, Jul 26, 2013 at 06:41:27AM +0100, vijay.kilari at gmail.com wrote: >>> From: Vijaya Kumar K <Vijaya.Kumar at caviumnetworks.com> >>> >>> In case of normal kexec kernel load, all cpu's are offlined >>> before calling machine_kexec() under kernel_kexec() function. >>> But in case crash panic cpus are relaxed in >>> machine_crash_nonpanic_core() SMP function but not offlined. >>> >>> When crash kernel is loaded with kexec and on panic trigger >>> machine_kexec() checks for number of cpus online. >>> If more than one cpu is online machine_kexec() fails to load >>> with below error >>> >>> kexec: error: multiple CPUs still online >>> >>> In machine_crash_nonpanic_core() SMP function, offline CPU >>> before cpu_relax > >>> diff --git a/arch/arm/kernel/machine_kexec.c b/arch/arm/kernel/machine_kexec.c > >>> @@ -73,6 +73,7 @@ void machine_crash_nonpanic_core(void *unused) >>> crash_save_cpu(®s, smp_processor_id()); >>> flush_cache_all(); >>> >>> + set_cpu_online(smp_processor_id(), false); >>> atomic_dec(&waiting_for_crash_ipi); >>> while (1) >>> cpu_relax(); >> >> Ok, I guess this will work since the new kernel is loaded somewhere higher >> in memory and the crashed kernel will stick around, so the non-crashing CPUs >> can sit around spinning. > > Does a kernel that's used as the crash kernel guarantee: > > * Never to re-use the memory that was used by the previous kernel, so > that the spin loop code/data won't be corrupted, ever, no matter how > long the crash recovery kernel runs. > > * Not use SMP, so there's never a need to re-activate the non-boot CPUs, > which might not work if they aren't truly disabled but rather just > running a pin loop? >From cat /proc/iomem, normal kernel is executed from (0x80xxxxxx) with crash kernel reserved 64M at 0xa0000000 80000000-bfffffff : System RAM 80008000-805aeddf : Kernel code 805e2000-8063e427 : Kernel data a0000000-a3ffffff : Crash kernel crash kernel is loaded to reserved memory location and is executed from there. I could confirm this from /proc/iomem when crash kernel is running a0000000-a3efffff : System RAM a0008000-a05aeddf : Kernel code a05e2000-a063e427 : Kernel data
