Re: [PATCH v2] module: check if memory leak by module.

[Miroslav Benes]

On Wed, 29 Mar 2017, Michal Hocko wrote:

> On Wed 29-03-17 11:32:02, Maninder Singh wrote:
> > This patch checks if any module which is going to be unloaded
> > is doing vmalloc memory leak or not.
> 
> Hmm, how can you track _all_ vmalloc allocations done on behalf of the
> module? It is quite some time since I've checked kernel/module.c but
> from my vague understading your check is basically only about statically
> vmalloced areas by module loader. Is that correct? If yes then is this
> actually useful? Were there any bugs in the loader code recently? What
> led you to prepare this patch? All this should be part of the changelog!

Moreover, I don't understand one thing:
  
> > Logs:-
> > [  129.336368] Module [test_module] is getting unloaded before doing vfree

ok, but...

> > +static void check_memory_leak(struct module *mod)
> > +{
> > +	struct vmap_area *va;
> > +
> > +	rcu_read_lock();
> > +	list_for_each_entry_rcu(va, &vmap_area_list, list) {
> > +		if (!(va->flags & VM_VM_AREA))
> > +			continue;
> > +		if ((mod->core_layout.base < va->vm->caller) &&
> > +			(mod->core_layout.base + mod->core_layout.size) > va->vm->caller) {
> > +			pr_err("Module [%s] is getting unloaded before doing vfree\n", mod->name);
> > +			pr_err("Memory still allocated: addr:0x%lx - 0x%lx, pages %u\n",
> > +				va->va_start, va->va_end, va->vm->nr_pages);
> > +			pr_err("Allocating function %pS\n", va->vm->caller);
> > +		}
> > +
> > +	}
> > +	rcu_read_unlock();
> > +}
> > +
> >  /* Free a module, remove from lists, etc. */
> >  static void free_module(struct module *mod)
> >  {
> > +	check_memory_leak(mod);
> > +

Of course, vfree() has not been called yet. It is the beginning of 
free_module(). vfree() is one of the last things you need to do. See 
module_memfree(). If I am not missing something, you get pr_err() 
everytime a module is unloaded.

Regards,
Miroslav