[Xen-devel] FALSE ALARM Re: Xen crash during boot with debug=y

[George Dunlap <George.Dunlap@xxxxxxxxxxxxx>]

Seems I did the first build with debug=n, and subsequent builds with
debug=y (apparently) didn't catch pci.c.  Modifying the file at all
caused it to be recompiled, which changed the spinkock init code
properly.

Second afternoon wasted chasing a didn't-make-mrproper bug...

 -George

On Tue, Jun 2, 2009 at 6:19 PM, George Dunlap
<George.Dunlap@xxxxxxxxxxxxx> wrote:
> Hm, I added some code to the check_lock() to print whenever it was
> initializing, and found that the lock in pci.c was initialized to
> zero.
>
> So I added some code to double-check the lock, modifying the layout of
> pci.c slightly, and the problem went away.
>
> Which likely means that there's a buffer overflow somewhere clobbering
> the spinlock debug value.  Fun, fun, fun...
>
>  -George
>
> On Tue, Jun 2, 2009 at 4:09 PM, George Dunlap
> <George.Dunlap@xxxxxxxxxxxxx> wrote:
>> I'm getting the following panic in Xen with tip when building with
>> debug=y.  It seems to be something with the spinlock/irq
>> sanity-checking code; but it doesn't make any sense, because the lock
>> in question is defined statically in xen/arch/x86/pci.c, and only used
>> two places in that file, with irqsave/irqrestore both times.  Any
>> ideas?
>>
>>  -George
>>
>> (XEN) Freed 140kB init memory.
>> (XEN) Xen BUG at spinlock.c:24
>> (XEN) ----[ Xen-3.5-unstable  x86_64  debug=y  Tainted:    C ]----
>> (XEN) CPU:    0
>> (XEN) RIP:    e008:[<ffff828c8011b7b7>] check_lock+0x3d/0x49
>> (XEN) RFLAGS: 0000000000010046   CONTEXT: hypervisor
>> (XEN) rax: 0000000000000000   rbx: ffff828c8020fa68   rcx: 0000000000000001
>> (XEN) rdx: 0000000000000000   rsi: 0000000000000001   rdi: ffff828c8020fa6c
>> (XEN) rbp: ffff828c8028fd38   rsp: ffff828c8028fd38   r8:  0000000000000000
>> (XEN) r9:  ffff828c8028fee4   r10: 0000000000cfbb00   r11: 000000000000ffff
>> (XEN) r12: 0000000000000286   r13: 0000000000000004   r14: 0000000000000000
>> (XEN) r15: 0000000000000000   cr0: 000000008005003b   cr4: 00000000000026f0
>> (XEN) cr3: 000000012ffae000   cr2: 00000000c1013fe8
>> (XEN) ds: e021   es: e021   fs: 0000   gs: 0000   ss: 0000   cs: e008
>> (XEN) Xen stack trace from rsp=ffff828c8028fd38:
>> (XEN)    ffff828c8028fd58 ffff828c8011ba2f 0000000000000004 0000000080000008
>> (XEN)    0000000000000000 ffff828c80161187 0000000000000004 ffff828c8028fdb8
>> (XEN)    0000000000000cfc ffff828c80167ba2 ffff8300cf2fa000 0000000000000000
>> (XEN)    0000000000000cfc ffff828c8028fe88 ffff828c8028ff28 0000000000000000
>> (XEN)    ffff828c8028ff18 ffff828c8016b11c ffff83010000f800 ffff8300cf2fa000
>> (XEN)    ffff828c8028fe78 ffff828c8015e527 ffff828c8028fe28 0000000000000282
>> (XEN)    0000000000000282 0000000000000286 000000008028fe58 ffff83012ffc6308
>> (XEN)    ffff83012feb9a80 0000000000000006 00000000ff750000 ffff8300cf2fa000
>> (XEN)    ffff828c8028fe78 ffff828c80162f66 000000000000e021 ffff828402000020
>> (XEN)    ffff83012feb9a80 0000000000000006 00000004025fd720 0000000400000004
>> (XEN)    00000000c0603d87 ffff828c8015ebf6 828c801db970b948 c390ed90d1ffffff
>> (XEN)    00000000ff750000 000000008011d687 000000012feb9067 ffff83012ffcc0e0
>> (XEN)    ffff828c8028ffed 00000000ffffffff 0000000000000000 ffff8300cf2fa000
>> (XEN)    0000000000000000 00c0bb0000000000 0000000000000000 ffff8300cf2fa000
>> (XEN)    0000000000000000 0000000000000000 0000000000000000 0000000000000000
>> (XEN)    00007d737fd700b7 ffff828c801db6db 0000000000000000 0000000000000000
>> (XEN)    0000000000000000 0000000000000000 00000000c05f3f34 0000000000000cfc
>> (XEN)    0000000000000000 0000000000000000 0000000000000000 0000000000000000
>> (XEN)    0000000000000000 0000000000000000 0000000000000cfc 0000000000000000
>> (XEN)    0000000000000000 0000000d00000000 00000000c0603d86 000000000000e019
>> (XEN) Xen call trace:
>> (XEN)    [<ffff828c8011b7b7>] check_lock+0x3d/0x49
>> (XEN)    [<ffff828c8011ba2f>] _spin_lock_irqsave+0x21/0x53
>> (XEN)    [<ffff828c80161187>] pci_conf_read+0x37/0xd0
>> (XEN)
>> (XEN)
>> (XEN) ****************************************
>> (XEN) Panic on CPU 0:
>> (XEN) Xen BUG at spinlock.c:24
>> (XEN) ****************************************
>> (XEN)
>> (XEN) Reboot in five seconds...
>>
>

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