Re: [PATCH v3 2/5] alloc_tag: load module tags into separate contiguous memory

Andrew Morton
2024-10-14T23:51:51Z

On Mon, 14 Oct 2024 13:36:43 -0700 Suren Baghdasaryan <surenb@google.com> wrote:

> When a module gets unloaded there is a possibility that some of the
> allocations it made are still used and therefore the allocation tags
> corresponding to these allocations are still referenced. As such, the
> memory for these tags can't be freed. This is currently handled as an
> abnormal situation and module's data section is not being unloaded.
> To handle this situation without keeping module's data in memory,
> allow codetags with longer lifespan than the module to be loaded into
> their own separate memory. The in-use memory areas and gaps after
> module unloading in this separate memory are tracked using maple trees.
> Allocation tags arrange their separate memory so that it is virtually
> contiguous and that will allow simple allocation tag indexing later on
> in this patchset. The size of this virtually contiguous memory is set
> to store up to 100000 allocation tags.
>
> ...
>
> --- a/kernel/module/main.c
> +++ b/kernel/module/main.c
> @@ -1254,22 +1254,17 @@ static int module_memory_alloc(struct module *mod, enum mod_mem_type type)
> return 0;
> }
>
> -static void module_memory_free(struct module *mod, enum mod_mem_type type,
> - bool unload_codetags)
> +static void module_memory_free(struct module *mod, enum mod_mem_type type)
> {
> struct module_memory *mem = &mod->mem[type];
> - void *ptr = mem->base;
>
> if (mem->is_rox)
> vfree(mem->rw_copy);
>
> - if (!unload_codetags && mod_mem_type_is_core_data(type))
> - return;
> -
> - execmem_free(ptr);
> + execmem_free(mem->base);
> }

The changes around here are dependent upon Mike's "module: make
module_memory_{alloc,free} more self-contained", which is no longer in
mm-unstable. I assume Mike is working on a v2 so I'll park this series
for now.