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

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Message-Id: <20241014165149.6adebbf38fdc0a1f79ded66b@linux-foundation.org>
Date: Mon, 14 Oct 2024 16:51:49 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Suren Baghdasaryan <surenb@...gle.com>
Cc: kent.overstreet@...ux.dev, corbet@....net, arnd@...db.de,
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Subject: Re: [PATCH v3 2/5] alloc_tag: load module tags into separate
 contiguous memory

On Mon, 14 Oct 2024 13:36:43 -0700 Suren Baghdasaryan <surenb@...gle.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.