[Crash-utility] [PATCH 2/3] crash: ARM: get online CPUs from cpu_active_mask

[Dave Anderson]

----- Original Message -----
> For ARM32 platfrom, The system will "offline" all CPUs except the
> crashing one, by clear the cpu_online_mask. So we need to find
> another way to get online-CPUs number for crash utility.
> 
> This patch uses cpu_active_mask to get that value.
> 
> Signed-off-by: Liu Hua <sdu.liu at huawei.com>
> ---
>  arm.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arm.c b/arm.c
> index 3c38cd5..c94d7bf 100644
> --- a/arm.c
> +++ b/arm.c
> @@ -1518,7 +1518,7 @@ arm_display_machine_stats(void)
>  static int
>  arm_get_smp_cpus(void)
>  {
> -	return get_cpus_online();
> +	return get_cpus_active();
>  }
>  
>  /*

When did this start happening?  I ask because no other ARM users have 
reported this until now.  I've only got one sample SMP vmcore, and 
clearly the non-crashing cpu was not offlined:

  crash> sys
        KERNEL: /usr/dumps/ARM/vmlinux.smp.gz
      DUMPFILE: /usr/dumps/ARM/vmcore.smp
          CPUS: 2
          DATE: Fri Dec 31 19:00:37 1999
        UPTIME: 00:00:33
  LOAD AVERAGE: 0.00, 0.00, 0.00
         TASKS: 31
      NODENAME: ME.mop500
       RELEASE: 2.6.36-rc6-next-20101005-00033-g5d269a5-dirty
       VERSION: #20 SMP PREEMPT Fri Oct 8 10:34:09 CEST 2010
       MACHINE: armv7l  (unknown Mhz)
        MEMORY: 88 MB
         PANIC: "Internal error: Oops: 817 [#1] PREEMPT SMP" (check log for details)
  crash>
  
The non-panicking cpu was issued an IPI to shutdown:
  
  crash> bt -a
  PID: 0      TASK: c03eebc0  CPU: 0   COMMAND: "swapper"
   #0 [<c01ddda0>] (machine_crash_nonpanic_core) from [<c0216754>]
   #1 [<c0216754>] (generic_smp_call_function_single_interrupt) from [<c01d3270>]
   #2 [<c01d3270>] (do_IPI) from [<c01d8388>]
      pc : [<c01d9a1c>]    lr : [<c01d9a18>]    psr: 60000013
      sp : c03d3fc8  ip : c4bae044  fp : 00000000
      r10: 00000000  r9 : 411fc091  r8 : 0001e3fc
      r7 : c03efbb4  r6 : c01cfb3c  r5 : c03ff4e0  r4 : c03d2000
      r3 : 00000000  r2 : c03d3fc8  r1 : 00000001  r0 : c4ba09c0
      Flags: nZCv  IRQs on  FIQs on  Mode SVC_32  ISA ARM
   #3 [<c01d8388>] (__irq_svc) from [<c01d9a18>]
   #4 [<c01d9a1c>] (default_idle) from [<c01d9f3c>]
   #5 [<c01d9f3c>] (cpu_idle) from [<c0008b28>]
   #6 [<c0008b28>] (start_kernel) from [<00008038>]
  
  PID: 408    TASK: c5195e00  CPU: 1   COMMAND: "sh"
   #0 [<c03071ec>] (sysrq_handle_crash) from [<c03076ac>]
   #1 [<c03076ac>] (__handle_sysrq) from [<c030777c>]
   #2 [<c030777c>] (write_sysrq_trigger) from [<c028943c>]
   #3 [<c028943c>] (proc_reg_write) from [<c024d4bc>]
   #4 [<c024d4bc>] (vfs_write) from [<c024d5e4>]
   #5 [<c024d5e4>] (sys_write) from [<c01d8880>]
      pc : [<401f0c6c>]    lr : [<401a9b70>]    psr: 60000010
      sp : bea07598  ip : 00000002  fp : 0007dd00
      r10: 0000000a  r9 : 00000000  r8 : 00000002
      r7 : 00000004  r6 : 4009a000  r5 : 00000002  r4 : 40258650
      r3 : 00000000  r2 : 00000002  r1 : 4009a000  r0 : 00000001
      Flags: nZCv  IRQs on  FIQs on  Mode USER_32  ISA ARM
  crash> 
  
And as expected, the cpu_online mask shows both cpus:
  
  crash> help -k
  ... [ cut ] ...
         cpu_possible_map: 0 1 
          cpu_present_map: 0 1 
           cpu_online_map: 0 1 
  ...


Also, backwards-compatibility must be maintained, and it appears that
the cpu_active mask was only first introduced in 2.6.27.  So perhaps it
should be something like:

--- arm.c.orig	2014-04-25 14:44:23.557665220 -0400
+++ arm.c	2014-04-25 15:13:46.709594145 -0400
@@ -1518,7 +1518,7 @@
 static int
 arm_get_smp_cpus(void)
 {
-	return get_cpus_online();
+	return MAX(get_cpus_active(), get_cpus_online());
 }
 
Dave