Re: [PATCH v2 27/28] binder: reverse locking order in shrinker callback

[Carlos Llamas]

On Mon, Dec 04, 2023 at 11:57:42AM +0000, 'Alice Ryhl' via kernel-team wrote:
> > +	trace_binder_unmap_kernel_start(alloc, index);
> > +
> > +	page_to_free = page->page_ptr;
> > +	page->page_ptr = NULL;
> > +
> > +	trace_binder_unmap_kernel_end(alloc, index);
> 
> What are these trace calls used for? Previously they wrapped the call to
> __free_page, and happened after the `trace_binder_unmap_user_*` calls.
> 

It also used to wrap an unmap_kernel_range() call, which explains the
naming of the tracepoint I suppose. It looked like this:

	trace_binder_unmap_kernel_start(alloc, index);

	unmap_kernel_range(page_addr, PAGE_SIZE);
	__free_page(page->page_ptr);
	page->page_ptr = NULL;

	trace_binder_unmap_kernel_end(alloc, index);

My thinking was that we care more about the page->page_ptr clearing but
it sounds like we could just drop the tracepoint, we no longer have a
kernel mapped area.

--
Carlos Llamas