linux-kernel - Re: [PATCH v4 2/6] binder: Store lru freelist in binder

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Message-ID: <202507162323.8A11B97@keescook>
Date: Wed, 16 Jul 2025 23:23:56 -0700
From: Kees Cook <kees@...nel.org>
To: Tiffany Yang <ynaffit@...gle.com>
Cc: linux-kernel@...r.kernel.org, kernel-team@...roid.com,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Arve Hjønnevåg <arve@...roid.com>,
	Todd Kjos <tkjos@...roid.com>, Martijn Coenen <maco@...roid.com>,
	Joel Fernandes <joelagnelf@...dia.com>,
	Christian Brauner <brauner@...nel.org>,
	Carlos Llamas <cmllamas@...gle.com>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Brendan Higgins <brendan.higgins@...ux.dev>,
	David Gow <davidgow@...gle.com>, Rae Moar <rmoar@...gle.com>,
	linux-kselftest@...r.kernel.org, kunit-dev@...glegroups.com
Subject: Re: [PATCH v4 2/6] binder: Store lru freelist in binder_alloc

On Wed, Jul 16, 2025 at 06:10:05PM -0700, Tiffany Yang wrote:
> Store a pointer to the free pages list that the binder allocator should
> use for a process inside of struct binder_alloc. This change allows
> binder allocator code to be tested and debugged deterministically while
> a system is using binder; i.e., without interfering with other binder
> processes and independently of the shrinker. This is necessary to
> convert the current binder_alloc_selftest into a kunit test that does
> not rely on hijacking an existing binder_proc to run.
> 
> A binder process's binder_alloc->freelist should not be changed after
> it is initialized. A sole exception is the process that runs the
> existing binder_alloc selftest. Its freelist can be temporarily replaced
> for the duration of the test because it runs as a single thread before
> any pages can be added to the global binder freelist, and the test frees
> every page it allocates before dropping the binder_selftest_lock. This
> exception allows the existing selftest to be used to check for
> regressions, but it will be dropped when the binder_alloc tests are
> converted to kunit in a subsequent patch in this series.
> 
> Acked-by: Carlos Llamas <cmllamas@...gle.com>
> Signed-off-by: Tiffany Yang <ynaffit@...gle.com>

Reviewed-by: Kees Cook <kees@...nel.org>

-- 
Kees Cook