Re: KASAN-related VMAP allocation errors in debug kernels with many logical CPUS

[David Hildenbrand <david@redhat.com>]

>>> Maybe try to increase the module-section size to see if it solves the
>>> problem.
>>
>> What would be the easiest way to do that?
>>
> Sorry for late answer. I was trying to reproduce it on my box. What i
> did was trying to load all modules in my system with KASAN_INLINE option:
> 

Thanks!

> <snip>
> #!/bin/bash
> 
> # Exclude test_vmalloc.ko
> MODULES_LIST=(`find /lib/modules/$(uname -r) -type f \
> 	\( -iname "*.ko" -not -iname "test_vmalloc*" \) | awk -F"/" '{print $NF}' | sed 's/.ko//'`)
> 
> function moduleExist(){
> 	MODULE="$1"
> 	if lsmod | grep "$MODULE" &> /dev/null ; then
> 		return 0
> 	else
> 		return 1
> 	fi
> }
> 
> i=0
> 
> for module_name in ${MODULES_LIST[@]}; do
> 	sudo modprobe $module_name
> 
> 	if moduleExist ${module_name}; then
> 		((i=i+1))
> 		echo "Successfully loaded $module_name counter $i"
> 	fi
> done
> <snip>
> 
> as you wrote it looks like it is not easy to reproduce. So i do not see
> any vmap related errors.

Yeah, it's quite mystery and only seems to trigger on these systems with 
a lot of CPUs.

> 
> Returning back to the question. I think you could increase the MODULES_END
> address and shift the FIXADDR_START little forward. See the dump_pagetables.c
> But it might be they are pretty compact and located in the end. So i am not
> sure if there is a room there.

That's what I was afraid of :)

> 
> Second. It would be good to understand if vmap only fails on allocating for a
> module:
> 
> <snip>
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index dd6cdb201195..53026fdda224 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -1614,6 +1614,8 @@ static struct vmap_area *alloc_vmap_area(unsigned long size,
>          va->va_end = addr + size;
>          va->vm = NULL;
>   
> +       trace_printk("-> alloc %lu size, align: %lu, vstart: %lu, vend: %lu\n", size, align, vstart, vend);
> +
>          spin_lock(&vmap_area_lock);
> <snip>

I'll try grabbing a suitable system again and add some more debugging 
output. Might take a while, unfortunately.

-- 
Thanks,

David / dhildenb