Public bug reported:

Create VM on Azure using Canonical UbuntuServer 14.04.5-LTS latest using
size Standard DS2 v2

Install kexec-tools kdump-tools makedumpfile, configure boot kernel
parameter crashkernel=512M

Run sed -i 's/USE_KDUMP=0/USE_KDUMP=1/g' /etc/default/kdump-tools and
sed -i 's/LOAD_KEXEC=true/LOAD_KEXEC=false/g' /etc/default/kexec

Reboot VM, make sure crash kernel memory reserved successfully

Trigger a crash by run echo 1 > /proc/sys/kernel/sysrq, then echo c >
/proc/sysrq-trigger, VM will reboot automatically and after reboot,
check crash dump is generated under /var/crash

Install linux-azure kernel

Enable private-ppa canonical-kernel-esm

Install kernel linux-azure, reboot VM, kernel version 4.15.0-1084-azure

Trigger a crash by run echo 1 > /proc/sys/kernel/sysrq, then echo c >
/proc/sysrq-trigger, VM entered into a hung status.

Attach whole serial console
[   65.452007] INFO: rcu_sched detected stalls on CPUs/tasks:
[   65.456004]  1-...!: (0 ticks this GP) idle=488/0/0 softirq=1/1 fqs=0
[   65.456004]  (detected by 0, t=15002 jiffies, g=707, c=706, q=8457)
[   65.456004] rcu_sched kthread starved for 15002 jiffies! g707 c706 f0x0 
RCU_GP_WAIT_FQS(3) ->state=0x402 ->cpu=1
[  360.020026] INFO: rcu_sched detected stalls on CPUs/tasks:
[  360.024015]  1-...!: (10 GPs behind) idle=b34/0/0 softirq=1/1 fqs=1
[  360.024015]  (detected by 0, t=15002 jiffies, g=717, c=716, q=6429)
[  360.024015] rcu_sched kthread starved for 15000 jiffies! g717 c716 f0x0 
RCU_GP_WAIT_FQS(3) ->state=0x402 ->cpu=1
[  420.048010] INFO: rcu_sched detected stalls on CPUs/tasks:
[  420.052006]  1-...!: (0 ticks this GP) idle=f94/0/0 softirq=1/1 fqs=0
[  420.052006]  (detected by 0, t=15002 jiffies, g=718, c=717, q=6429)
[  420.052006] rcu_sched kthread starved for 15002 jiffies! g718 c717 f0x0 
RCU_GP_WAIT_FQS(3) ->state=0x402 ->cpu=1

** Affects: linux-azure (Ubuntu)
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1882623

Title:
  VM enter into hung status after triggering a crash

Status in linux-azure package in Ubuntu:
  New

Bug description:
  Create VM on Azure using Canonical UbuntuServer 14.04.5-LTS latest
  using size Standard DS2 v2

  Install kexec-tools kdump-tools makedumpfile, configure boot kernel
  parameter crashkernel=512M

  Run sed -i 's/USE_KDUMP=0/USE_KDUMP=1/g' /etc/default/kdump-tools and
  sed -i 's/LOAD_KEXEC=true/LOAD_KEXEC=false/g' /etc/default/kexec

  Reboot VM, make sure crash kernel memory reserved successfully

  Trigger a crash by run echo 1 > /proc/sys/kernel/sysrq, then echo c >
  /proc/sysrq-trigger, VM will reboot automatically and after reboot,
  check crash dump is generated under /var/crash

  Install linux-azure kernel

  Enable private-ppa canonical-kernel-esm

  Install kernel linux-azure, reboot VM, kernel version
  4.15.0-1084-azure

  Trigger a crash by run echo 1 > /proc/sys/kernel/sysrq, then echo c >
  /proc/sysrq-trigger, VM entered into a hung status.

  Attach whole serial console
  [   65.452007] INFO: rcu_sched detected stalls on CPUs/tasks:
  [   65.456004]  1-...!: (0 ticks this GP) idle=488/0/0 softirq=1/1 fqs=0
  [   65.456004]  (detected by 0, t=15002 jiffies, g=707, c=706, q=8457)
  [   65.456004] rcu_sched kthread starved for 15002 jiffies! g707 c706 f0x0 
RCU_GP_WAIT_FQS(3) ->state=0x402 ->cpu=1
  [  360.020026] INFO: rcu_sched detected stalls on CPUs/tasks:
  [  360.024015]  1-...!: (10 GPs behind) idle=b34/0/0 softirq=1/1 fqs=1
  [  360.024015]  (detected by 0, t=15002 jiffies, g=717, c=716, q=6429)
  [  360.024015] rcu_sched kthread starved for 15000 jiffies! g717 c716 f0x0 
RCU_GP_WAIT_FQS(3) ->state=0x402 ->cpu=1
  [  420.048010] INFO: rcu_sched detected stalls on CPUs/tasks:
  [  420.052006]  1-...!: (0 ticks this GP) idle=f94/0/0 softirq=1/1 fqs=0
  [  420.052006]  (detected by 0, t=15002 jiffies, g=718, c=717, q=6429)
  [  420.052006] rcu_sched kthread starved for 15002 jiffies! g718 c717 f0x0 
RCU_GP_WAIT_FQS(3) ->state=0x402 ->cpu=1

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