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

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Date:   Mon, 4 Dec 2023 15:47:22 +0100
From:   Alice Ryhl <aliceryhl@...gle.com>
To:     Carlos Llamas <cmllamas@...gle.com>
Cc:     arve@...roid.com, brauner@...nel.org, gregkh@...uxfoundation.org,
        joel@...lfernandes.org, kernel-team@...roid.com,
        linux-kernel@...r.kernel.org, maco@...roid.com, surenb@...gle.com,
        tkjos@...roid.com
Subject: Re: [PATCH v2 27/28] binder: reverse locking order in shrinker callback

On Mon, Dec 4, 2023 at 3:45 PM Carlos Llamas <cmllamas@...gle.com> wrote:
>
> 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.

Ok. Feel free to remove or move the trace calls however it needs to be
done and add my tag:

Reviewed-by: Alice Ryhl <aliceryhl@...gle.com>