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Dave Hansen wrote: > 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: >> >> http://sr71.net/~dave/linux/2.6.26-oops1.txt >> > > I think I found it!!! > > $ (objdump -d kvm.ko ; objdump -d kvm-intel.ko ) | egrep 'sub.*0x...,.*esp|>:' | egrep sub -B1 > 00001a90 <kvm_vcpu_ioctl>: > 1a9a: 81 ec 60 06 00 00 sub $0x660,%esp > -- > 00004e90 <kvm_arch_vcpu_ioctl>: > 4e9d: 81 ec 6c 08 00 00 sub $0x86c,%esp > -- > 00005900 <kvm_arch_vm_ioctl>: > 5903: 81 ec 34 05 00 00 sub $0x534,%esp > -- > 0000d4f0 <paging64_prefetch_page>: > d4f8: 81 ec 1c 01 00 00 sub $0x11c,%esp > -- > 0000dfd0 <paging32_prefetch_page>: > dfd8: 81 ec 1c 01 00 00 sub $0x11c,%esp > -- > 0000f390 <kvm_pv_mmu_op>: > f3a1: 81 ec 28 02 00 00 sub $0x228,%esp > > We're simply overflowing the stack. I changed all of the large on-stack > allocations to 'static', and it actually boots now. I know 'static' > isn't safe, but it was good for a quick test. > > Yes! It's obvious, once you know it... > A 'make stackcheck' confirms this: > > dave@nimitz:~/kernels/linux-2.6.git$ 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? > Yes, things like kvm_lapic_state are way too big to be on the stack. There's an additional problem here, that apparently your gcc (which version?) doesn't fold objects in a switch statement into the same stack slot: switch (...) { case x: { struct medium a; ... } case y: struct medium b; ... } }; These could be solved either by stack allocation, or by moving into functions marked noinline. Whichever is easier. -- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain. | ||||||||||||
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