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From:   Liam Howlett <liam.howlett@oracle.com>
To:     Carlos Llamas <cmllamas@google.com>
CC:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        =?iso-8859-1?Q?Arve_Hj=F8nnev=E5g?= <arve@android.com>,
        Todd Kjos <tkjos@android.com>,
        Martijn Coenen <maco@android.com>,
        Joel Fernandes <joel@joelfernandes.org>,
        Christian Brauner <brauner@kernel.org>,
        Suren Baghdasaryan <surenb@google.com>,
        "kernel-team@android.com" <kernel-team@android.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 4/7] binder: remove binder_alloc_set_vma()
Thread-Topic: [PATCH 4/7] binder: remove binder_alloc_set_vma()
Thread-Index: AQHYu+PDQMrZoK0Qy0yO8Kcq2Jru363HzQaA
Date:   Tue, 30 Aug 2022 18:57:59 +0000
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 <20220829201254.1814484-5-cmllamas@google.com>
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* Carlos Llamas <cmllamas@google.com> [220829 16:13]:
> The mmap_locked asserts here are not needed since this is only called
> back from the mmap stack in ->mmap() and ->close() which always acquire
> the lock first. Remove these asserts along with binder_alloc_set_vma()
> altogether since it's trivial enough to be consumed by callers.

I agree that it is not called anywhere else today.  I think it's still
worth while since these asserts do nothing if you don't build with
lockdep and/or debug_vm enabled.  I was hoping having these here would
avoid future mistakes a lot like what we have in the mm code's
find_vma() (mm/mmap.c ~L2297).


>=20
> Cc: Liam R. Howlett <Liam.Howlett@oracle.com>
> Signed-off-by: Carlos Llamas <cmllamas@google.com>
> ---
>  drivers/android/binder_alloc.c | 25 ++-----------------------
>  1 file changed, 2 insertions(+), 23 deletions(-)
>=20
> diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_allo=
c.c
> index 749a4cd30a83..1c39cfce32fa 100644
> --- a/drivers/android/binder_alloc.c
> +++ b/drivers/android/binder_alloc.c
> @@ -309,27 +309,6 @@ static int binder_update_page_range(struct binder_al=
loc *alloc, int allocate,
>  	return vma ? -ENOMEM : -ESRCH;
>  }
> =20
> -
> -static inline void binder_alloc_set_vma(struct binder_alloc *alloc,
> -		struct vm_area_struct *vma)
> -{
> -	unsigned long vm_start =3D 0;
> -
> -	/*
> -	 * Allow clearing the vma with holding just the read lock to allow
> -	 * munmapping downgrade of the write lock before freeing and closing th=
e
> -	 * file using binder_alloc_vma_close().
> -	 */
> -	if (vma) {
> -		vm_start =3D vma->vm_start;
> -		mmap_assert_write_locked(alloc->mm);
> -	} else {
> -		mmap_assert_locked(alloc->mm);
> -	}
> -
> -	alloc->vma_addr =3D vm_start;
> -}
> -
>  static inline struct vm_area_struct *binder_alloc_get_vma(
>  		struct binder_alloc *alloc)
>  {
> @@ -793,7 +772,7 @@ int binder_alloc_mmap_handler(struct binder_alloc *al=
loc,
>  	buffer->free =3D 1;
>  	binder_insert_free_buffer(alloc, buffer);
>  	alloc->free_async_space =3D alloc->buffer_size / 2;
> -	binder_alloc_set_vma(alloc, vma);
> +	alloc->vma_addr =3D vma->vm_start;
> =20
>  	return 0;
> =20
> @@ -983,7 +962,7 @@ int binder_alloc_get_allocated_count(struct binder_al=
loc *alloc)
>   */
>  void binder_alloc_vma_close(struct binder_alloc *alloc)
>  {
> -	binder_alloc_set_vma(alloc, NULL);
> +	alloc->vma_addr =3D 0;
>  }
> =20
>  /**
> --=20
> 2.37.2.672.g94769d06f0-goog
> =