linux-kernel - Re: [PATCH v2 19/28] binder: perform page installation outside of locks

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Message-ID: <20231204115712.41114-1-aliceryhl@google.com>
Date:   Mon,  4 Dec 2023 11:57:11 +0000
From:   Alice Ryhl <aliceryhl@...gle.com>
To:     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, Alice Ryhl <aliceryhl@...gle.com>
Subject: Re: [PATCH v2 19/28] binder: perform page installation outside of locks

> Split out the insertion of pages to be outside of the alloc->mutex in a
> separate binder_install_buffer_pages() routine. Since this is no longer
> serialized, we must look at the full range of pages used by the buffers.
> The installation is protected with mmap_sem in write mode since multiple
> tasks might race to install the same page.
> 
> Besides avoiding unnecessary nested locking this helps in preparation of
> switching the alloc->mutex into a spinlock_t in subsequent patches.
> 
> Signed-off-by: Carlos Llamas <cmllamas@...gle.com>

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

> +static inline struct page *
> +binder_get_installed_page(struct binder_lru_page *lru_page)
> +{
> +	/* Pairs with release in binder_set_installed_page() */
> +	return smp_load_acquire(&lru_page->page_ptr);
> +}

Technically some of the uses of this method do not actually need to be
atomic (because they never race with `binder_set_installed_page`), but I
don't mind using it anyway.

Alice