On Wed, 2008-07-16 at 14:44 -0700, Dave Hansen wrote:
On a suggestion of Anthony's, I tried a defconfig kernel.
It is now bombing out on an assertion in the lapic code:
I think I found it!!!
$ (objdump -d kvm.ko ; objdump -d kvm-intel.ko ) | egrep 'sub.*0x...,.*esp|>:' | egrep sub -B1
1a9a: 81 ec 60 06 00 00 sub $0x660,%esp
4e9d: 81 ec 6c 08 00 00 sub $0x86c,%esp
5903: 81 ec 34 05 00 00 sub $0x534,%esp
d4f8: 81 ec 1c 01 00 00 sub $0x11c,%esp
dfd8: 81 ec 1c 01 00 00 sub $0x11c,%esp
f3a1: 81 ec 28 02 00 00 sub $0x228,%esp
We're simply overflowing the stack. I changed all of the large on-stack
allocations to 'static', and it actually boots now. I know 'static'
isn't safe, but it was good for a quick test.
A 'make stackcheck' confirms this:
dave@nimitz:~/kernels/linux-2.6.git$ make checkstack
objdump -d vmlinux $(find . -name '*.ko') | \
perl /home/dave/kernels/linux-2.6.git-t61/scripts/checkstack.pl i386
0x000042d3 kvm_arch_vcpu_ioctl [kvm]: 2148
0x000012e3 kvm_vcpu_ioctl [kvm]: 1620
0x00004a83 kvm_arch_vm_ioctl [kvm]: 1332
0x00009a26 airo_get_aplist [airo]: 1140
0x00009b76 airo_get_aplist [airo]: 1140
0x00009c82 airo_get_aplist [airo]: 1140
In other words, kvm has the top 3 stack users in my kernel. As you can
see from my trace above, these things also get called with super-long
stacks already. Man. That sucked to find.
Avi, how would you like this fixed? I'd be happy to prepare some
patches. Do you have a particular approach that you think we should
use? Just make the big objects dynamically allocated?