Re: [PATCH 1/2] boot: increase stack size for kernel boot loader decompressor

[Mike Travis <travis@sgi.com>]

Ingo Molnar wrote:
> * Alexander van Heukelum <heukelum@mailshack.com> wrote:
> 
>> I did see that the malloc space that the inflate code is using is 
>> taken from _after_ the end of the bss. I don't see how this is 
>> protected from being used/overwritten. Changing the stack size changes 
>> the memory layout a bit... maybe you were so unlucky to create a 
>> vmlinux image that was just barely smaller than some threshold and 
>> increasing the stack size made the decompression/relocation area be 
>> located somewhere else?
>>
>> Test patch follows.
> 
> that's a really interesting theory.
> 
> FWIIW, i've been booting allyesconfig bzImages for a long time (with 
> only minimal amount of drivers disabled - mostly old ISA ones that 
> assume the presence of the real hardware), and they boot and work fine 
> on both 32-bit and 64-bit typical whitebox PCs. That means huge bzImages 
> that decompresses into a ~41 MB kernel image. I'd expect that to be a 
> rather severe test of the decompressor.
> 
> 	Ingo

Well admittedly, I did discover this problem way early in booting
up a 4k NR_CPU kernel (obviously ;-).  Once it booted, I haven't
revisited that problem again.  I wonder if it's a pathological case
of a single bitstream that causes expansion instead of compression?
Note I was using the akpm2 config script with NR_CPUS=4096 and
NODES_SHIFT=9 (plus some other tweaks specific to our AMD and Intel
boxes.)

Thanks,
Mike