soft lockup in kvm_flush_remote_tlbs

[david ahern <daahern-FYB4Gu1CFyUAvxtiuMwx3w@public.gmane.org>]

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();
	}

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

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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