[BUG] Module load relocation hashtable size can become huge and unallocatable

[William Pierce]

Using vmalloc_array/vfree on the relocation_hashtable
allows the kernel module to load just fine. I can send this
as a patch if the fix sounds good.

On 3/30/25 1:12 PM, William Pierce wrote:
> Hello, I have a kernel module that requires a huge number
> of relocations upon loading.
> 
> On other architectures, it loads into the kernel just fine.
> However, on riscv, while allocating memory for its relocation
> hashtable, it ends up requesting 2097152 elements to kmalloc_array.
> 
> Right here I've dumped the values by recompiling the kernel:
> num_relocations: 1630985, hastable_size: 2097152
> https://elixir.bootlin.com/linux/v6.14-rc6/source/arch/riscv/kernel/module.c#L734
> 
> which kmalloc_array->...->___kmalloc_large_node->...->
> __alloc_frozen_pages_noprof can't handle and returns
> "Cannot allocate memory" on insmod.
> 
> How would it be recommended to fix this?
> I could imagine allocating a more discontiguous data structure
> to track the relocations or otherwise reworking the tracking to
> do the relocation tracking inline.
> 
> Thank you,
> Will Pierce