From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: soft lockup in kvm_flush_remote_tlbs Date: Thu, 25 Oct 2007 08:47:07 +0200 Message-ID: <47203BEB.9070509@qumranet.com> References: <471FCEA6.6000903@cisco.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: kvm-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org To: david ahern Return-path: In-Reply-To: <471FCEA6.6000903-FYB4Gu1CFyUAvxtiuMwx3w@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org Errors-To: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org List-Id: kvm.vger.kernel.org david ahern wrote: > 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! > [] softlockup_tick+0x98/0xa6 > [] update_process_times+0x39/0x5c > [] smp_apic_timer_interrupt+0x5c/0x64 > [] apic_timer_interrupt+0x1f/0x24 > [] kvm_flush_remote_tlbs+0xce/0xdb [kvm] > [] kvm_mmu_pte_write+0x1f2/0x368 [kvm] > [] emulator_write_emulated_onepage+0x73/0xe6 [kvm] > [] x86_emulate_insn+0x20d8/0x3348 [kvm] > [] x86_decode_insn+0x624/0x872 [kvm] > [] emulate_instruction+0x12b/0x258 [kvm] > [] handle_exception+0x163/0x23f [kvm_intel] > [] kvm_handle_exit+0x70/0x8a [kvm_intel] > [] kvm_vcpu_ioctl_run+0x234/0x339 [kvm] > [] kvm_vcpu_ioctl+0x0/0xa8f [kvm] > [] kvm_vcpu_ioctl+0xbd/0xa8f [kvm] > [] save_i387+0x23f/0x273 > [] __next_cpu+0x12/0x21 > [] find_busiest_group+0x177/0x462 > [] setup_sigcontext+0x10d/0x190 > [] get_page_from_freelist+0x96/0x310 > [] get_page_from_freelist+0x2a6/0x310 > [] flush_tlb_others+0x83/0xb3 > [] flush_tlb_page+0x74/0x77 > [] set_page_dirty_balance+0x8/0x35 > [] do_wp_page+0x3a5/0x3bd > [] dequeue_signal+0x2d/0x9c > [] __handle_mm_fault+0x81b/0x87b > [] kvm_vcpu_ioctl+0x0/0xa8f [kvm] > [] do_ioctl+0x1c/0x5d > [] vfs_ioctl+0x24a/0x25c > [] sys_ioctl+0x48/0x5f > [] 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. > > I don't think it's a cpu not responding. I've stared at the code for a while (we had this before) and the actual IPI/ack is fine. What's probably happening is that corruption of the mmu data structures is causing kvm_flush_remote_tlbs() to be called repeatedly. Since it's a very slow function, the lockup detector blames it for any lockup it sees even though it is innocent. [we had exactly this issue before and it was indeed fixed after an rmap corruption was corrected] > 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. > > > - please send (privately, it's big) an 'objdump -Sr' of mmu.o - what guest are you running? if it's publicly available, I can try to replicate it - at what stage does the failure occur? if it's early on, we can try running with AUDIT or DEBUG - otherwise, I'll send debugging patches to try and see what's going on -- Any sufficiently difficult bug is indistinguishable from a feature. ------------------------------------------------------------------------- This SF.net email is sponsored by: Splunk Inc. Still grepping through log files to find problems? Stop. Now Search log events and configuration files using AJAX and a browser. Download your FREE copy of Splunk now >> http://get.splunk.com/