Re: soft lockup in kvm_flush_remote_tlbs

[Laurent Vivier <Laurent.Vivier-6ktuUTfB/bM@public.gmane.org>]

david ahern a écrit :
> I am trying, unsuccessfully so far, to get a vm running with 4 cpus. It is failing with a soft lockup:
> 
> BUG: soft lockup detected on CPU#3!
>  [<c044a05f>] softlockup_tick+0x98/0xa6
>  [<c042ccd4>] update_process_times+0x39/0x5c
>  [<c04176ec>] smp_apic_timer_interrupt+0x5c/0x64
>  [<c04049bf>] apic_timer_interrupt+0x1f/0x24
>  [<f8a3c800>] kvm_flush_remote_tlbs+0xce/0xdb [kvm]
>  [<f8a41a72>] kvm_mmu_pte_write+0x1f2/0x368 [kvm]
>  [<f8a3d335>] emulator_write_emulated_onepage+0x73/0xe6 [kvm]
>  [<f8a4542c>] x86_emulate_insn+0x20d8/0x3348 [kvm]
>  [<f8a43106>] x86_decode_insn+0x624/0x872 [kvm]
>  [<f8a3d764>] emulate_instruction+0x12b/0x258 [kvm]
>  [<f88af2e4>] handle_exception+0x163/0x23f [kvm_intel]
>  [<f88af09b>] kvm_handle_exit+0x70/0x8a [kvm_intel]
>  [<f8a3deae>] kvm_vcpu_ioctl_run+0x234/0x339 [kvm]
>  [<f8a3e27f>] kvm_vcpu_ioctl+0x0/0xa8f [kvm]
>  [<f8a3e33c>] kvm_vcpu_ioctl+0xbd/0xa8f [kvm]
>  [<c0408f60>] save_i387+0x23f/0x273
>  [<c04db730>] __next_cpu+0x12/0x21
>  [<c041c97f>] find_busiest_group+0x177/0x462
>  [<c04031cd>] setup_sigcontext+0x10d/0x190
>  [<c0453bed>] get_page_from_freelist+0x96/0x310
>  [<c0453dfd>] get_page_from_freelist+0x2a6/0x310
>  [<c0415a5c>] flush_tlb_others+0x83/0xb3
>  [<c0415d63>] flush_tlb_page+0x74/0x77
>  [<c0454cf1>] set_page_dirty_balance+0x8/0x35
>  [<c0459c1b>] do_wp_page+0x3a5/0x3bd
>  [<c042e97e>] dequeue_signal+0x2d/0x9c
>  [<c045af6b>] __handle_mm_fault+0x81b/0x87b
>  [<f8a3e27f>] kvm_vcpu_ioctl+0x0/0xa8f [kvm]
>  [<c0479cac>] do_ioctl+0x1c/0x5d
>  [<c0479f37>] vfs_ioctl+0x24a/0x25c
>  [<c0479f91>] sys_ioctl+0x48/0x5f
>  [<c0403eff>] syscall_call+0x7/0xb
> 
> 
> I am working with kvm-48, but also tried the 20071020 snapshot. The stuck code is kvm_flush_remote_tlbs():
> 
> 	while (atomic_read(&completed) != needed) {
> 		cpu_relax();
> 		barrier();
> 	}
> 

This part has been removed by commit 49d3bd7e2b990e717aa66e229410b8f5096c4956, 
perhaps you could try it ?

commit 49d3bd7e2b990e717aa66e229410b8f5096c4956
Author: Laurent Vivier <Laurent.Vivier-6ktuUTfB/bM@public.gmane.org>
Date:   Mon Oct 22 16:33:07 2007 +0200

     KVM: Use new smp_call_function_mask() in kvm_flush_remote_tlbs()

     In kvm_flush_remote_tlbs(), replace a loop using smp_call_function_single()
     by a single call to smp_call_function_mask() (which is new for x86_64).

     Signed-off-by: Laurent Vivier <Laurent.Vivier-6ktuUTfB/bM@public.gmane.org>
     Signed-off-by: Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org>

> which I take to mean one of the CPUs is not ack'ing the TLB flush request. 

Yes, it seems...

> Is this is a known bug and any options to correct it? It works fine with 2 vcpus, but for a comparison with xen I'd like to get the vm working with 4.
> 
> 
> Host stats:
> OS: RHEL5
> Processors: 2-Core 2 Duos (4 processors)
> KVM:  kvm-48 and kvm-20071020-1 snapshot rpms
> QEMU command:
> 
> qemu-kvm -boot c -localtime -hda /opt/kvm/images/cucm.img -m 1536 -smp 4 -serial file:/tmp/serial.log -net nic,macaddr=00:1a:4b:34:74:52,model=rtl8139 -net tap,ifname=tap0,script=/bin/true -vnc :2 -monitor stdio
> 
> 
> thanks,
> 
> david
> 
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-- 
---------------- Laurent.Vivier-6ktuUTfB/bM@public.gmane.org  -----------------
"Given enough eyeballs, all bugs are shallow" E. S. Raymond


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