At Mon, 23 Mar 2015 18:46:45 +0100,
Denys Vlasenko wrote:
>
> On 03/23/2015 06:18 PM, Takashi Iwai wrote:
> > At Mon, 23 Mar 2015 17:07:15 +0100, Denys Vlasenko wrote:
> >>>> I pulled tip tree on top of 4.0-rc5, built with your patch and now
> >>>> succeeded to get a better message:
> >>>>
> >>>> kvm: zapping shadow pages for mmio generation wraparound
> >>>> kvm [5126]: vcpu0 disabled perfctr wrmsr: 0xc1 data 0xffff
> >>>> Exception on user stack 00007ffd22c23ef0: RSP: 0018:00007ffd22c23f28
> >>>> EFLAGS: 00010006
> >>>> RIP: 0010:[<ffffffff8162681d>] [<ffffffff8162681d>]
> >>>> netlink_attachskb+0x1d/0x1d0
> >>>> PANIC: double fault, error_code: 0x0
> >>>> CPU: 1 PID: 10819 Comm: cc1 Tainted: G W 4.0.0-rc5-debug1+
> >>>> #2
> >>>> Hardware name: Dell Inc. OptiPlex 9010/0M9KCM, BIOS A12 01/10/2013
> >>>> task: ffff8800d1b34b10 ti: ffff8800d1b30000 task.ti: ffff8800d1b30000
> >>>> RIP: 0010:[<ffffffff8162681d>] [<ffffffff8162681d>]
> >>>> netlink_attachskb+0x1d/0x1d0
> >>>> RSP: 0018:00007ffd22c23f28 EFLAGS: 00010006
> >>>> RAX: 0000000000000000 RBX: 0000000000000005 RCX: 00000000c0000101
> >>>> RDX: 0000000000000000 RSI: 0000000000000001 RDI: 00007ffd22c23ef0
>
> >> FYI: the disassembly of netlink_attachskb (from "Code:" line) is:
> >>
> >> 0: 0f 1f 44 00 00 nopl 0x0(%rax,%rax,1)
> >> 5: 55 push %rbp
> >> 6: 48 89 e5 mov %rsp,%rbp
> >> 9: 41 56 push %r14
> >> b: 41 55 push %r13
> >> d: 49 89 d5 mov %rdx,%r13
> >> 10: 41 54 push %r12
> >> 12: 49 89 f4 mov %rsi,%r12
> >> 15: 53 push %rbx
> >> 16: 48 89 fb mov %rdi,%rbx
> >> 19: 48 83 ec 30 sub $0x30,%rsp
> >> 1d: 8b 87 68 01 00 00 mov 0x168(%rdi),%eax
> >> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> >> 23: 39 87 9c 01 00 00 cmp %eax,0x19c(%rdi)
> >> 29: 7c 25 jl 50 <_start+0x50>
> >> 2b: 48 8b 87 88 04 00 00 mov 0x488(%rdi),%rax
> >>
> >> The ^^^^^ instruction is the one which faults. Since you said it
> >> consistently happens here, this should be a page fault, not an external
> >> hardware interrupt.
> >>
> >> The code corresponds to the comparison in if():
> >>
> >> int netlink_attachskb(struct sock *sk, struct sk_buff *skb,
> >> long *timeo, struct sock *ssk)
> >> {
> >> struct netlink_sock *nlk;
> >>
> >> nlk = nlk_sk(sk);
> >>
> >> if ((atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf ||
>
> >>> - Another piece is that the bug happens only when a KVM is running.
> >>> The kernel ran without problem over days with similar tasks
> >>> (compiling kernel, etc) when no KVM was used.
> >>
> >> Conceivably virtualization support in CPUs can have nasty erratas.
> >> However, you and other reporter have different CPUs - yours
> >> is Ivy Bridge, his CPU is a Penryn.
> >>
> >> I don't see the path how KVM helps to trigger this.
> >>
> >>> - And now I get the trace as above, pointing netlink_attachskb().
> >>>
> >>> I have a difficulty to imagine how all these pieces fit into a single
> >>> picture. Is something already screwed up before that?
> >>
> >> Well, a tiny bit more info will be seen if you'd change %rdi
> >> to, say, %r15 in these two lines in my patch:
> >>
> >> /* Save bogus RSP value */
> >> movq %rsp,%rdi
> >> ...
> >> push %rdi /* pt_regs->sp */
> >>
> >> Then original %rdi will be visible in the crash message.
> >
> > OK, here we go.
> >
> > kvm: zapping shadow pages for mmio generation wraparound
> > kvm [5490]: vcpu0 disabled perfctr wrmsr: 0xc1 data 0xffff
> > Exception on user stack 00007fff1d7e5ec0: RSP: 0018:00007fff1d7e5ef8
> > EFLAGS: 00010002
> > RIP: 0010:[<ffffffff8162681d>] [<ffffffff8162681d>]
> > netlink_attachskb+0x1d/0x1d0
> > PANIC: double fault, error_code: 0x0
> > CPU: 5 PID: 14285 Comm: fixdep Tainted: G W 4.0.0-rc5-debug1+
> > #3
> > Hardware name: Dell Inc. OptiPlex 9010/0M9KCM, BIOS A12 01/10/2013
> > task: ffff88020ba1c690 ti: ffff880206ba4000 task.ti: ffff880206ba4000
> > RIP: 0010:[<ffffffff8162681d>] [<ffffffff8162681d>]
> > netlink_attachskb+0x1d/0x1d0
> > RSP: 0018:00007fff1d7e5ef8 EFLAGS: 00010002
> > RAX: 0000000000000000 RBX: 0000000000000000 RCX: 00000000c0000101
> > RDX: 0000000000000000 RSI: 0000000000001ebb RDI: 0000000000000000
>
> Thanks for your testing. So the %rdi was NULL... not very informative.
>
> Notice that your every crash is preceded by
>
> kvm: zapping shadow pages for mmio generation wraparound
> kvm [5490]: vcpu0 disabled perfctr wrmsr: 0xc1 data 0xffff
>
> This hints that kvm _is_ somehow responsible.
It's likely irrelevant, as this appears at the time a VM starting, not
at the crash time. I've got this message all the time. Sorry for
confusing.
Takashi
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