[Xen-ia64-devel] [PATCH] fix soft lock up caused by xen_timer_interrupt()

[Atsushi SAKAI <sakaia@xxxxxxxxxxxxxx>]

Hi

 This patch intends to fix softlockup caused by xen_timer_interrupt().
This is caused by local_cpu_data->itm_next and stime_irq, itc_at_irq 
inconsistency at CPU0 of hypervisor.
This patch sets stime_irq and itc_at_irq every time
in xen_timer_interrupt() to avoid this soft lock up.

In other words, it caused by 
competition of local_cpu_data->itm_next and domain_itm in 
xen_timer_interrupt() and reprogram_timer()(more specific 
vcpu_set_next_timer()).

For example, 
1)reprogram_timer() runs and set local_cpu_data->itm_next
  and set domain_itm as next itm.
2)xen_timer_interrupt() called but not satisfied following condition.   
while(time_after(ia64_get_itc(),local_cpu_data->itm_next)
  Then skip stime_irq and itc_at_irq setting.
3)goto 1)
4) sometimes local_cpu_data->itm_next is rollback 
  because ns_to_cycle()/IA64 is representing almost 32bit.
  (This is occured at reprogram_timer())
5)It causes soft lock up.
6)Hypervisor returns to work(not hang).

To reproduce this issue, I do following configuration.

1) boot Xen with pcpu=4 and Dom0 with vcpu=4
2) boot domU1 with vcpu with vcpu-pin 0-1
3) boot domU2 with vcpu with vcpu-pin 0-1
4) run yes > /dev/null  2 process on domU1
5) run nothing on domU2(to check softlock up occured or not)
6) run kernel compile with -j4 on Dom0 continuously
7) wait 4 or 8 hours to occur softlockup.

Signed-off-by: Atsushi SAKAI <sakaia@xxxxxxxxxxxxxx>

Thanks
Atsushi SAKAI

Attachment: fix_softlockup.patch
Description: Binary data

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