Re: qemu-kvm-1.1.0 crashing with kernel 3.5.0-rc6

[Chris Clayton <chris2553@googlemail.com>]

On 07/19/12 19:23, Chris Clayton wrote:
> On 07/19/12 13:17, Avi Kivity wrote:
>> On 07/19/2012 03:14 PM, Chris Clayton wrote:
>>
>>>> Change of diagnostics, unfortunately. qemu-kvm-1.0.1 can, in fact,
>>>> crash
>>>> on 3.5.0-rc6 (and rc7). I didn't get it earlier because it takes many
>>>> times more invocations before the crash occurs with 1.0.1 and I haven't
>>>> used qemu-kvm much in the past few weeks.
>>>>
>>>> I'm now checking whether I can get crashes (with 1.0.1 and/or 1.1.0) on
>>>> linux-3.4.4. I'll report back in a day or two.
>>>
>>> I've started up qemu-kvm on kernel 3.4.4 many times and not see a crash.
>>> That would indicate that the problem is in the kernel. However, I pulled
>>> the latest and greatest from Linus yesterday evening and I now can't get
>>> the crash there either, so whatever it was seems to have been fixed. If
>>> I checkout and build 3.5.0-rc[1..7], I can get the crash pretty quickly,
>>> so it's been fixed in the last few days.
>>
>> There were no kvm changes post-rc7.
>>
> Yes, I'm aware of that, Avi. This thread started because I was getting a
> crash in qemu-kvm, which I thought was only in v1.1.0. Later it turned
> out the the problem was also present in v1.0.1, but much harder to hit.
> However, it only ever happened with 3.5.0 kernels. 3.4.4, with either
> version of qemu-kvm, was stable. So then it seemed that the problem was
> in the kernel, (but not necessarily in the kvm code).
>
> Something that's changed since rc7 has either fixed the problem or made
> it much harder to hit. With rc7 and earlier I can recreate the crash
> quite easily with qemu-kvm-1.1.0 and with enough runs of 1.0.1. With
> rc7+, I haven't been able to get a crash at all.
>
Well, I'm getting the crash again, but this time I've managed to get a 
backtrace:

Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0xb60ffb40 (LWP 9405)]
0xb7803d77 in __strcmp_sse4_2 () from /lib/libc.so.6
(gdb) bt
#0  0xb7803d77 in __strcmp_sse4_2 () from /lib/libc.so.6
#1  0xb7e65333 in g_str_equal () from /usr/lib/libglib-2.0.so.0
#2  0xb7e6458d in g_hash_table_lookup () from /usr/lib/libglib-2.0.so.0
#3  0x8014e2cf in type_table_lookup (name=0x802b0c50 "apic-common") at 
qom/object.c:94
#4  type_get_by_name (name=name@entry=0x802b0c50 "apic-common") at 
qom/object.c:149
#5  0x8014e933 in object_dynamic_cast (obj=obj@entry=0x80a5d818, 
typename=typename@entry=0x802b0c50 "apic-common")
     at qom/object.c:416
#6  0x8014e8b9 in object_dynamic_cast_assert (obj=obj@entry=0x80a5d818,
     typename=typename@entry=0x802b0c50 "apic-common") at qom/object.c:478
#7  0x80193462 in cpu_set_apic_tpr (d=0x80a5d818, val=8 '\b')
     at /home/chris/rpm/BUILD/qemu-kvm-1.1.1/hw/apic_common.c:60
#8  0x801d0560 in kvm_arch_post_run (env=env@entry=0x80a55a60, 
run=run@entry=0xb6239000)
     at /home/chris/rpm/BUILD/qemu-kvm-1.1.1/target-i386/kvm.c:1695
#9  0x801cb05f in kvm_cpu_exec (env=env@entry=0x80a55a60) at 
/home/chris/rpm/BUILD/qemu-kvm-1.1.1/kvm-all.c:1269
#10 0x80199d1e in qemu_kvm_cpu_thread_fn (arg=0x80a55a60) at 
/home/chris/rpm/BUILD/qemu-kvm-1.1.1/cpus.c:752
#11 0xb7a1fd9e in start_thread () from /lib/libpthread.so.0
#12 0xb77bbbbe in clone () from /lib/libc.so.6

This is with kernel 3.5.0 and qemu-kvm-1.1.1. glibc is 2.16.0 built 
against 3.4.4 kernel headers. The glibc, the kernel headers and the 
kernel are vanilla and the only change to the qemu-kvm sources is:

--- qemu-kvm-1.1.0/configure~   2012-07-15 22:38:39.000000000 +0100
+++ qemu-kvm-1.1.0/configure    2012-07-15 22:39:09.000000000 +0100
@@ -2783,7 +2783,7 @@ int main(int argc, char **argv)
  }
  EOF
    if ! compile_prog "" "" ; then
-    CFLAGS+="-march=i486"
+    CFLAGS+="-march=i686"
    fi
  fi

Please let me know of anything I can do to help track this down.

Thanks

Chris

> I'm not inclined to bisect to find out which patch provided the fix, but
> this mail should at least close the mail thread down tidily.
>
> Chris